diff --git a/packages/vitest/src/runtime/mocker.ts b/packages/vitest/src/runtime/mocker.ts
index 105c5c145a06..b3543c731719 100644
--- a/packages/vitest/src/runtime/mocker.ts
+++ b/packages/vitest/src/runtime/mocker.ts
@@ -328,7 +328,7 @@ export class VitestMocker {
           const spyModule = this.spyModule
           if (!spyModule)
             throw this.createError('[vitest] `spyModule` is not defined. This is Vitest error. Please open a new issue with reproduction.')
-          const mock = spyModule.spyOn(newContainer, property).mockImplementation(function (this: any, ...args: any[]) {
+          const mock = spyModule.spyOn(newContainer, property).mockImplementation(function (this: any) {
             // jest reference
             // https://github.com/jestjs/jest/blob/2c3d2409879952157433de215ae0eee5188a4384/packages/jest-mock/src/index.ts#L678-L691
 
@@ -339,9 +339,9 @@ export class VitestMocker {
               for (const key in this) {
                 if (typeof this[key] === 'function') {
                   // TODO: ability to restore?
-                  // mock but delegate to original prototype method, which should be also mocked already
+                  // mock by delegating calls to original prototype method, which should be also mocked already
                   const original = this[key]
-                  spyModule.spyOn(this, key).mockImplementation(() => original.apply(this, args))
+                  const _mockInner = spyModule.spyOn(this, key).mockImplementation((...args: any[]) => original.apply(this, args))
                 }
               }
             }
diff --git a/test/core/src/mockedE.ts b/test/core/src/mockedE.ts
index dcdeb479f319..607a90bdc1b3 100644
--- a/test/core/src/mockedE.ts
+++ b/test/core/src/mockedE.ts
@@ -1,5 +1,5 @@
 export class MockedE {
-  public doSomething(arg: string) {
+  public testFn(arg: string) {
     return arg.repeat(2)
   }
 }
diff --git a/test/core/test/mocked-wip.test.ts b/test/core/test/mocked-wip.test.ts
index 4e9327bd3b40..ba7ceef7803a 100644
--- a/test/core/test/mocked-wip.test.ts
+++ b/test/core/test/mocked-wip.test.ts
@@ -12,23 +12,83 @@ test('mock each instance method separately', () => {
   const instance1 = new MockedE()
   const instance2 = new MockedE()
   expect(instance1).not.toBe(instance2)
-  expect(instance1.doSomething).not.toBe(instance2.doSomething)
-  expect(instance1.doSomething).not.toBe(MockedE.prototype.doSomething)
-  expect(vi.mocked(instance1.doSomething).mock).not.toBe(vi.mocked(instance2.doSomething).mock)
-
-  // TODO: check input/output
-  instance1.doSomething('a')
-  expect(instance1.doSomething).toBeCalledTimes(1)
-  expect(instance2.doSomething).toBeCalledTimes(0)
-  expect(MockedE.prototype.doSomething).toBeCalledTimes(1)
-
-  instance2.doSomething('b')
-  expect(instance1.doSomething).toBeCalledTimes(1)
-  expect(instance2.doSomething).toBeCalledTimes(1)
-  expect(MockedE.prototype.doSomething).toBeCalledTimes(2)
-
-  instance1.doSomething('c')
-  expect(instance1.doSomething).toBeCalledTimes(2)
-  expect(instance2.doSomething).toBeCalledTimes(1)
-  expect(MockedE.prototype.doSomething).toBeCalledTimes(3)
+  expect(instance1.testFn).not.toBe(instance2.testFn)
+  expect(instance1.testFn).not.toBe(MockedE.prototype.testFn)
+  expect(vi.mocked(instance1.testFn).mock).not.toBe(vi.mocked(instance2.testFn).mock)
+
+  instance1.testFn('a')
+  expect(instance1.testFn).toBeCalledTimes(1)
+  expect(instance2.testFn).toBeCalledTimes(0)
+  expect(MockedE.prototype.testFn).toBeCalledTimes(1)
+  expect(vi.mocked(instance1.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "a",
+      ],
+    ]
+  `)
+  expect(vi.mocked(MockedE.prototype.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "a",
+      ],
+    ]
+  `)
+
+  instance2.testFn('b')
+  expect(instance1.testFn).toBeCalledTimes(1)
+  expect(instance2.testFn).toBeCalledTimes(1)
+  expect(MockedE.prototype.testFn).toBeCalledTimes(2)
+  expect(vi.mocked(instance2.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "b",
+      ],
+    ]
+  `)
+  expect(vi.mocked(MockedE.prototype.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "a",
+      ],
+      [
+        "b",
+      ],
+    ]
+  `)
+
+  instance1.testFn('c')
+  expect(instance1.testFn).toBeCalledTimes(2)
+  expect(instance2.testFn).toBeCalledTimes(1)
+  expect(MockedE.prototype.testFn).toBeCalledTimes(3)
+  expect(vi.mocked(instance1.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "a",
+      ],
+      [
+        "c",
+      ],
+    ]
+  `)
+  expect(vi.mocked(instance2.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "b",
+      ],
+    ]
+  `)
+  expect(vi.mocked(MockedE.prototype.testFn).mock.calls).toMatchInlineSnapshot(`
+    [
+      [
+        "a",
+      ],
+      [
+        "b",
+      ],
+      [
+        "c",
+      ],
+    ]
+  `)
 })