diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index cc6a9e6db9a..7c125d72e99 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -900,9 +900,7 @@ namespace ts {
     }
 
     export function fileExtensionIs(path: string, extension: string): boolean {
-        const pathLen = path.length;
-        const extLen = extension.length;
-        return pathLen > extLen && path.substr(pathLen - extLen, extLen) === extension;
+        return path.length > extension.length && endsWith(path, extension);
     }
 
     export function fileExtensionIsAny(path: string, extensions: string[]): boolean {
@@ -915,7 +913,6 @@ namespace ts {
         return false;
     }
 
-
     // Reserved characters, forces escaping of any non-word (or digit), non-whitespace character.
     // It may be inefficient (we could just match (/[-[\]{}()*+?.,\\^$|#\s]/g), but this is future
     // proof.
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 151bac9ed62..c2a1e6ade66 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -112,13 +112,7 @@ namespace ts {
     }
 
     function moduleHasNonRelativeName(moduleName: string): boolean {
-        if (isRootedDiskPath(moduleName)) {
-            return false;
-        }
-
-        const i = moduleName.lastIndexOf("./", 1);
-        const startsWithDotSlashOrDotDotSlash = i === 0 || (i === 1 && moduleName.charCodeAt(0) === CharacterCodes.dot);
-        return !startsWithDotSlashOrDotDotSlash;
+        return !(isRootedDiskPath(moduleName) || isExternalModuleNameRelative(moduleName));
     }
 
     interface ModuleResolutionState {
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 6f3a1d6d813..f970a94373a 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1218,7 +1218,7 @@ namespace ts {
     export function isExternalModuleNameRelative(moduleName: string): boolean {
         // TypeScript 1.0 spec (April 2014): 11.2.1
         // An external module name is "relative" if the first term is "." or "..".
-        return moduleName.substr(0, 2) === "./" || moduleName.substr(0, 3) === "../" || moduleName.substr(0, 2) === ".\\" || moduleName.substr(0, 3) === "..\\";
+        return /^\.\.?($|[\\/])/.test(moduleName);
     }
 
     export function isInstantiatedModule(node: ModuleDeclaration, preserveConstEnums: boolean) {
@@ -3120,6 +3120,6 @@ namespace ts {
 
     export function endsWith(str: string, suffix: string): boolean {
         const expectedPos = str.length - suffix.length;
-        return str.indexOf(suffix, expectedPos) === expectedPos;
+        return expectedPos >= 0 && str.indexOf(suffix, expectedPos) === expectedPos;
     }
 }
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 6afb0cfccdb..534778fdab8 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -1377,31 +1377,27 @@ namespace Harness {
             writeByteOrderMark: boolean;
         }
 
-        function stringEndsWith(str: string, end: string) {
-            return str.substr(str.length - end.length) === end;
-        }
-
         export function isTS(fileName: string) {
-            return stringEndsWith(fileName, ".ts");
+            return ts.endsWith(fileName, ".ts");
         }
 
         export function isTSX(fileName: string) {
-            return stringEndsWith(fileName, ".tsx");
+            return ts.endsWith(fileName, ".tsx");
         }
 
         export function isDTS(fileName: string) {
-            return stringEndsWith(fileName, ".d.ts");
+            return ts.endsWith(fileName, ".d.ts");
         }
 
         export function isJS(fileName: string) {
-            return stringEndsWith(fileName, ".js");
+            return ts.endsWith(fileName, ".js");
         }
         export function isJSX(fileName: string) {
-            return stringEndsWith(fileName, ".jsx");
+            return ts.endsWith(fileName, ".jsx");
         }
 
         export function isJSMap(fileName: string) {
-            return stringEndsWith(fileName, ".js.map") || stringEndsWith(fileName, ".jsx.map");
+            return ts.endsWith(fileName, ".js.map") || ts.endsWith(fileName, ".jsx.map");
         }
 
         /** Contains the code and errors of a compilation and some helper methods to check its status. */
diff --git a/src/services/patternMatcher.ts b/src/services/patternMatcher.ts
index 93cc5130d72..3d20337eca7 100644
--- a/src/services/patternMatcher.ts
+++ b/src/services/patternMatcher.ts
@@ -514,16 +514,6 @@ namespace ts {
         return str === str.toLowerCase();
     }
 
-    function startsWith(string: string, search: string) {
-        for (let i = 0, n = search.length; i < n; i++) {
-            if (string.charCodeAt(i) !== search.charCodeAt(i)) {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
     // Assumes 'value' is already lowercase.
     function indexOfIgnoringCase(string: string, value: string): number {
         for (let i = 0, n = string.length - value.length; i <= n; i++) {
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.js b/tests/baselines/reference/relativeModuleWithoutSlash.js
new file mode 100644
index 00000000000..f83406499d4
--- /dev/null
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.js
@@ -0,0 +1,42 @@
+//// [tests/cases/compiler/relativeModuleWithoutSlash.ts] ////
+
+//// [a.ts]
+
+export default { a: 0 };
+
+//// [index.ts]
+export default { aIndex: 0 };
+
+//// [test.ts]
+import a from ".";
+import aIndex from "./";
+a.a;
+aIndex.a; //aIndex.aIndex; See GH#9690
+
+//// [test.ts]
+import a from "..";
+import aIndex from "../";
+a.a;
+aIndex.a; //aIndex.aIndex;
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;
+exports["default"] = { a: 0 };
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+exports["default"] = { aIndex: 0 };
+//// [test.js]
+"use strict";
+var _1 = require(".");
+var _2 = require("./");
+_1["default"].a;
+_2["default"].a; //aIndex.aIndex; See GH#9690
+//// [test.js]
+"use strict";
+var __1 = require("..");
+var _1 = require("../");
+__1["default"].a;
+_1["default"].a; //aIndex.aIndex;
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.symbols b/tests/baselines/reference/relativeModuleWithoutSlash.symbols
new file mode 100644
index 00000000000..434c3aa6bd7
--- /dev/null
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.symbols
@@ -0,0 +1,43 @@
+=== tests/cases/compiler/a.ts ===
+
+export default { a: 0 };
+>a : Symbol(a, Decl(a.ts, 1, 16))
+
+=== tests/cases/compiler/a/index.ts ===
+export default { aIndex: 0 };
+>aIndex : Symbol(aIndex, Decl(index.ts, 0, 16))
+
+=== tests/cases/compiler/a/test.ts ===
+import a from ".";
+>a : Symbol(a, Decl(test.ts, 0, 6))
+
+import aIndex from "./";
+>aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
+
+a.a;
+>a.a : Symbol(a, Decl(a.ts, 1, 16))
+>a : Symbol(a, Decl(test.ts, 0, 6))
+>a : Symbol(a, Decl(a.ts, 1, 16))
+
+aIndex.a; //aIndex.aIndex; See GH#9690
+>aIndex.a : Symbol(a, Decl(a.ts, 1, 16))
+>aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
+>a : Symbol(a, Decl(a.ts, 1, 16))
+
+=== tests/cases/compiler/a/b/test.ts ===
+import a from "..";
+>a : Symbol(a, Decl(test.ts, 0, 6))
+
+import aIndex from "../";
+>aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
+
+a.a;
+>a.a : Symbol(a, Decl(a.ts, 1, 16))
+>a : Symbol(a, Decl(test.ts, 0, 6))
+>a : Symbol(a, Decl(a.ts, 1, 16))
+
+aIndex.a; //aIndex.aIndex;
+>aIndex.a : Symbol(a, Decl(a.ts, 1, 16))
+>aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
+>a : Symbol(a, Decl(a.ts, 1, 16))
+
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.trace.json b/tests/baselines/reference/relativeModuleWithoutSlash.trace.json
new file mode 100644
index 00000000000..765389e4629
--- /dev/null
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.trace.json
@@ -0,0 +1,26 @@
+[
+    "======== Resolving module '.' from 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a'.",
+    "File 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts', result 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'",
+    "======== Module name '.' was successfully resolved to 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module './' from 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a'.",
+    "File 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts', result 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'",
+    "======== Module name './' was successfully resolved to 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module '..' from 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a/b/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a'.",
+    "File 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts', result 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'",
+    "======== Module name '..' was successfully resolved to 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'. ========",
+    "======== Resolving module '../' from 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a/b/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a'.",
+    "File 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for 'C:/Users/anhans/work/TypeScript/tests/cases/compiler/a.ts', result 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'",
+    "======== Module name '../' was successfully resolved to 'c:/users/anhans/work/typescript/tests/cases/compiler/a.ts'. ========"
+]
\ No newline at end of file
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.types b/tests/baselines/reference/relativeModuleWithoutSlash.types
new file mode 100644
index 00000000000..3b58f097405
--- /dev/null
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.types
@@ -0,0 +1,47 @@
+=== tests/cases/compiler/a.ts ===
+
+export default { a: 0 };
+>{ a: 0 } : { a: number; }
+>a : number
+>0 : number
+
+=== tests/cases/compiler/a/index.ts ===
+export default { aIndex: 0 };
+>{ aIndex: 0 } : { aIndex: number; }
+>aIndex : number
+>0 : number
+
+=== tests/cases/compiler/a/test.ts ===
+import a from ".";
+>a : { a: number; }
+
+import aIndex from "./";
+>aIndex : { a: number; }
+
+a.a;
+>a.a : number
+>a : { a: number; }
+>a : number
+
+aIndex.a; //aIndex.aIndex; See GH#9690
+>aIndex.a : number
+>aIndex : { a: number; }
+>a : number
+
+=== tests/cases/compiler/a/b/test.ts ===
+import a from "..";
+>a : { a: number; }
+
+import aIndex from "../";
+>aIndex : { a: number; }
+
+a.a;
+>a.a : number
+>a : { a: number; }
+>a : number
+
+aIndex.a; //aIndex.aIndex;
+>aIndex.a : number
+>aIndex : { a: number; }
+>a : number
+
diff --git a/tests/cases/compiler/relativeModuleWithoutSlash.ts b/tests/cases/compiler/relativeModuleWithoutSlash.ts
new file mode 100644
index 00000000000..3b4f50da306
--- /dev/null
+++ b/tests/cases/compiler/relativeModuleWithoutSlash.ts
@@ -0,0 +1,20 @@
+// @traceResolution: true
+// @moduleResolution: node
+
+// @Filename: a.ts
+export default { a: 0 };
+
+// @Filename: a/index.ts
+export default { aIndex: 0 };
+
+// @Filename: a/test.ts
+import a from ".";
+import aIndex from "./";
+a.a;
+aIndex.a; //aIndex.aIndex; See GH#9690
+
+// @Filename: a/b/test.ts
+import a from "..";
+import aIndex from "../";
+a.a;
+aIndex.a; //aIndex.aIndex;