Remove Page_Load event from content page.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        string script = "$(document).ready(function () { $('[id*=btnSubmit]').click(); });";
        ClientScript.RegisterStartupScript(this.GetType(), "load", script, true);
    }
}

Add a Button in master page and set Style="display: none;" with OnClick event.

<asp:Button ID="btnFake" Text="" Style="display: none;" runat="server" OnClick="SaveFake" />

Write the below code in master page.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        string script = "$(document).ready(function () { $('[id*=btnFake]').click(); });";
        Page.ClientScript.RegisterStartupScript(this.GetType(), "load", script, true);
    }
}

protected void SaveFake(object sender, EventArgs e)
{
    // Add Fake Delay to simulate long running process.
    System.Threading.Thread.Sleep(2000);
}