You may well find that the Framework ignores DestinationPageUrl and always redirects to the referring page, when the user is successfully authenticated.
To workaround this behavior, add a LoggedIn event handler (using Designer or manually in associated code file), that redirects to DestinationPageUrl, e.g.
protected void Login1_LoggedIn(object sender, EventArgs e)
{
// Manually redirect to DestinationPageUrl as Framework doesn't give property precedence over the
// referring page (ReturnUrl), which it should, according to Login.DestinationPageUrl documentation
Response.Redirect(ResolveClientUrl(Login1.DestinationPageUrl));
}
To hook up the event handler with the control (where you didn't use the Designer to add the event handler) add following attribute to Login tag:
<asp:Login runat="server" ID="Login1" DestinationPageUrl="~/MyPage.aspx" OnLoggedIn="Login1_LoggedIn">