Disable command button after 1 click

<asp:Button ID="ButtonConfirmOrder" runat="server" Text="Confirm Order" Width="129px" style="margin-left: 0px; color: #FFFFFF; background-color: #000000;" Height="27px" OnClick="ButtonConfirmOrder_Click" OnClientClick="return validation() OnClientClick="disableButton" ; /> <script> function disableButton() { document.getElementById('<%= ButtonConfirmOrder.ClientID %>').disabled = true; } </script> Hi folks, how do I disable this button after 1 click, keep getting error because OnClientClick has been used for something else, code below.