I have an autocomplete extender attached to a textbox that returns a single, most likely match after 2 characters are typed in the textbox. I would like the single match to automatically fill the textbox rather than having the user select the match from the dropdown (one item in dropdown).  Sort of what a combobox does.  I can't use a combobox because the list would be in the thousands. Is there anyway to do this? My code looks likes:

<td style="width:100px">Project Code:</td>
                                <td><asp:TextBox ID="txtProjCode" runat="server" CssClass="txtReadOnlyLeft" AutoPostBack="true"></asp:TextBox>
                                <asp:AutoCompleteExtender ID="autoProjCode" runat="server" ServicePath="~/AutoComplete.asmx"
                                        TargetControlID="txtProjCode" ServiceMethod="GetCompletionList"
                                        FirstRowSelected="true"
                                        MinimumPrefixLength="2" EnableCaching="true" ></asp:AutoCompleteExtender></td>