How do you call master page methods from a content page when the button is inside an update panel?

I think it's a bit late , but for those who are looking for the solution,

Assuming your master page class like:

public MyMAsterPage: MasterPage
{
    public void ShowMessage(string Message) 
    {
       // DO SOMETHING
    }
}

from your content page you can easily call any public method as follow:

(this.Master as MyMasterPage).ShowMessage("Some argument");

Function which define in masterpage:

public void Mesaj(string msj)
{
        lbl_Mesaj.Text = msj;
}

Function which define in content page

protected void Page_Load(object sender, EventArgs e)
{
    MasterPageWeb master = (MasterPageWeb)this.Master;
    master.Mesaj("www.zafercomert.com");
}

You can call masterpage's function from content page like this.

I ended up just sucking it up and putting the script manager on the master page and putting the label on the master page inside an update panel.