diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 168a201c388..cd378a889d2 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1394,14 +1394,18 @@ namespace ts {
         }
     }
 
-    export function copyListRemovingItem<T>(item: T, list: T[]) {
-        const copiedList: T[] = [];
-        for (const e of list) {
-            if (e !== item) {
-                copiedList.push(e);
+    export function removeItem<T>(item: T, array: T[]): void {
+        for (let i = 0; i < array.length; i++) {
+            if (array[i] === item) {
+                // Move everything over to the left.
+                // This seems to be faster than either `array.splice(i, 1)` or `array.copyWithin(i, i+ 1)`.
+                for (; i < array.length - 1; i++) {
+                    array[i] = array[i + 1];
+                }
+                array.pop();
+                break;
             }
         }
-        return copiedList;
     }
 
     export function createGetCanonicalFileName(useCaseSensitivefileNames: boolean): (fileName: string) => string {
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 350d75429b7..7953a2f42e8 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -285,13 +285,10 @@ namespace ts {
                 function removeFileWatcherCallback(filePath: string, callback: FileWatcherCallback) {
                     const callbacks = fileWatcherCallbacks[filePath];
                     if (callbacks) {
-                        const newCallbacks = copyListRemovingItem(callback, callbacks);
-                        if (newCallbacks.length === 0) {
+                        removeItem(callback, callbacks);
+                        if (callbacks.length === 0) {
                             delete fileWatcherCallbacks[filePath];
                         }
-                        else {
-                            fileWatcherCallbacks[filePath] = newCallbacks;
-                        }
                     }
                 }
 
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index a14c42f471e..0a12bf68d79 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -275,7 +275,7 @@ namespace ts.server {
         removeRoot(info: ScriptInfo) {
             if (this.filenameToScript.contains(info.path)) {
                 this.filenameToScript.remove(info.path);
-                this.roots = copyListRemovingItem(info, this.roots);
+                removeItem(info, this.roots);
                 this.resolvedModuleNames.remove(info.path);
                 this.resolvedTypeReferenceDirectives.remove(info.path);
             }
@@ -585,16 +585,6 @@ namespace ts.server {
         project?: Project;
     }
 
-    function copyListRemovingItem<T>(item: T, list: T[]) {
-        const copiedList: T[] = [];
-        for (let i = 0, len = list.length; i < len; i++) {
-            if (list[i] != item) {
-                copiedList.push(list[i]);
-            }
-        }
-        return copiedList;
-    }
-
     /**
      * This helper funciton processes a list of projects and return the concatenated, sortd and deduplicated output of processing each project.
      */
@@ -859,7 +849,7 @@ namespace ts.server {
                 project.directoryWatcher.close();
                 forEachValue(project.directoriesWatchedForWildcards, watcher => { watcher.close(); });
                 delete project.directoriesWatchedForWildcards;
-                this.configuredProjects = copyListRemovingItem(project, this.configuredProjects);
+                removeItem(project, this.configuredProjects);
             }
             else {
                 for (const directory of project.directoriesWatchedForTsconfig) {
@@ -871,7 +861,7 @@ namespace ts.server {
                         delete project.projectService.directoryWatchersForTsconfig[directory];
                     }
                 }
-                this.inferredProjects = copyListRemovingItem(project, this.inferredProjects);
+                removeItem(project, this.inferredProjects);
             }
 
             const fileNames = project.getFileNames();
@@ -996,7 +986,7 @@ namespace ts.server {
                 }
             }
             else {
-                this.openFilesReferenced = copyListRemovingItem(info, this.openFilesReferenced);
+                removeItem(info, this.openFilesReferenced);
             }
             info.close();
         }
@@ -1506,13 +1496,13 @@ namespace ts.server {
                             // openFileRoots or openFileReferenced.
                             if (info.isOpen) {
                                 if (this.openFileRoots.indexOf(info) >= 0) {
-                                    this.openFileRoots = copyListRemovingItem(info, this.openFileRoots);
+                                    removeItem(info, this.openFileRoots);
                                     if (info.defaultProject && !info.defaultProject.isConfiguredProject()) {
                                         this.removeProject(info.defaultProject);
                                     }
                                 }
                                 if (this.openFilesReferenced.indexOf(info) >= 0) {
-                                    this.openFilesReferenced = copyListRemovingItem(info, this.openFilesReferenced);
+                                    removeItem(info, this.openFilesReferenced);
                                 }
                                 this.openFileRootsConfigured.push(info);
                                 info.defaultProject = project;
diff --git a/src/server/server.ts b/src/server/server.ts
index 17ecfdaa1c9..b0f852b14f1 100644
--- a/src/server/server.ts
+++ b/src/server/server.ts
@@ -204,7 +204,7 @@ namespace ts.server {
     // average async stat takes about 30 microseconds
     // set chunk size to do 30 files in < 1 millisecond
     function createPollingWatchedFileSet(interval = 2500, chunkSize = 30) {
-        let watchedFiles: WatchedFile[] = [];
+        const watchedFiles: WatchedFile[] = [];
         let nextFileToCheck = 0;
         let watchTimer: any;
 
@@ -267,7 +267,7 @@ namespace ts.server {
         }
 
         function removeFile(file: WatchedFile) {
-            watchedFiles = copyListRemovingItem(file, watchedFiles);
+            removeItem(file, watchedFiles);
         }
 
         return {