@selectedValue

<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="@selectedValue">
</TelerikDropDownList>

@code {
    //in a real case, the model is usually in a separate file
    //the model type and value field type must be provided to the dropdpownlist
    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }

    IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });

    int selectedValue { get; set; }

    protected override void OnInitialized()
    {
        // workaround - set the value to the first item manually
        // this is done in OnInitialized for brevity, do it after fetching the data for the first time
        selectedValue = myDdlData.FirstOrDefault().MyValueField;

        base.OnInitialized();

    }
}