Where to pre set drop down list value when drop down box is populated with sqlDataSource in Gui

I have a drop down box on an Asp.net web form. The drop down box is loaded via a sql data source in the Aspx markup. Now in the C# code behind, I need to pre-set the drop down box to a certain value. If I try to set the value in the PageLoad or PreRender methods, I notice that the drop down list box has not yet been loaded through the data source.
So where at can I set the value of my drop down box?
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