public static void PerformClick(this Button button)
        {
            var peer =new ButtonAutomationPeer(button);

var invokeProv = peer.GetPattern(PatternInterface.Invoke) as IInvokeProvider;

if (invokeProv != null)
            {
                invokeProv.Invoke();
            }
        }

        public static void PerformClick(this UIElement element, Point point)
        {
            var window = Window.GetWindow(element);

if (window != null)
            {
                var windowHwnd = GetHwnd(window);

var locOfElement = element.TranslatePoint(new Point(0, 0), window);
                var pointToWindow = new Point(point.X + locOfElement.X, point.Y + locOfElement.Y);

Int32 lparam = MakeLong((int)pointToWindow.X, (int)pointToWindow.Y);

// WM_LBUTTONDOWN = 0x0201
                SendMessage(windowHwnd, WM_LBUTTONDOWN, 0, lparam);
                // WM_LBUTTONUP = 0x0202;
                SendMessage(windowHwnd, WM_LBUTTONUP, 0, lparam);
            }
        }

internal static int MakeLong(int lowWord, int highWord)
        {
            return (highWord << 16) | (lowWord & 0xffff);
        }

internal static IntPtr GetHwnd(this Window window)
        {
            var winHelper = new WindowInteropHelper(window);
            return winHelper.Handle;
        }

        public static void PerformClick(this ButtonBase button)
        {
            var method = button.GetType().GetMethod("OnClick", 
                BindingFlags.NonPublic | BindingFlags.Instance);

if (method != null)
            {
                method.Invoke(button, null);
            }

//button.Focus();
        }

 var sim = new InputSimulator();
 sim.Mouse.LeftButtonDown();