Web Forms :: 2.0 - Set Focus To A TextBox While Button Click Event Is Fired Using Default Button When Enter Key Is Pressed

How can I set Focus to a TextBox while Button click event is fired using Default Button when enter key is pressed. Here is my Page and code.

<%@ Page Title="" Language="C#" MasterPageFile="~/mpChat.master" AutoEventWireup="true" CodeFile="FocusTest.aspx.cs" Inherits="FocusTest" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Panel ID="Panel1" runat="server" DefaultButton="Button1">
<asp:TextBox ID="TextBox1" runat="server">
</asp:TextBox>
<asp:Button ID="Button1"
runat="server" Text="Button" onclick="Button1_Click" />
</asp:Panel>
</ContentTemplate>
</asp:UpdatePanel>
</asp:Content>
using System;
public partial class FocusTest : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
TextBox1.Focus();
}
protected void Button1_Click(object sender, EventArgs e)
{
TextBox1.Text = "";
TextBox1.Focus();
}
}