<telerik:RadComboBox ID="cmbDescription"  Filter="StartsWith" AllowCustomText="true" 

javascript:
function cmbDescription_OnClientDropDownOpening(sender, args) {
    var tempSLRef = grdVoucherItems.get_tempEntity().SLRef;
    if (currentSLRef !== tempSLRef) {
       
            currentSLRef = tempSLRef;
            PageMethods.FetchAllSLStandardDescBySLID(currentSLRef, AjaxFetchAllSLStandardDescSucceeded, OnPageMethodFailed, null);
       
    }
}
function AjaxFetchAllSLStandardDescSucceeded(result, context) {
    lstSlStandardDescs = result;
    cmbDescription.get_items().clear();
    for (var i = 0; i < lstSlStandardDescs.length; i++) {
        var comboItem = new Telerik.Web.UI.RadComboBoxItem();
        comboItem.set_text(lstSlStandardDescs[i].Item1);
        comboItem.set_value(lstSlStandardDescs[i].Item3);
        cmbDescription.trackChanges();
        cmbDescription.get_items().add(comboItem);
        cmbDescription.commitChanges();
        
    }

function

setFirstRowActive() {

var grid = $find("<%= grdCodeLists.ClientID %>");

var masterTable = grid.get_masterTableView();

var row;

//set first row as active

grid.set_activeRow(masterTable.get_dataItems()[0].get_element());

This only highlights the row but doesn't activiate it i.e. can't use up/down arrow to go up/down the rows. Instead of set_activeRow() i tried using SelectItem as well as set_selected properties but they produce the same results
How can this be achieved from both client and server side