Edit in JSFiddle

 $(function () {
     var availableCars = [
         "Renault Duster",
         "Maruti Swift",
         "Chevrolet Sail",
         "Maruti Swift Dzire",
         "Ford Figo",
         "Mahindra XUV 500",
         "Hyundai i20",
         "Volkswagen Polo",
         "Maruti Ertiga",
         "Hyundai EON",
         "Hyundai i10",
         "Maruti Wagon R",
         "Hyundai Verna ",
         "Fluidic",
         "Mahindra Scorpio",
         "Skoda Rapid"];
     var $cars = $('.cars');
     var $carsContainer = $('.containerForCars');
     $cars.autocomplete({
         source: availableCars
     });
     $($carsContainer[0].children[0].children[0]).focus();
 });

<p>The Cars text box gets the focus on page load.</p>
<div class="containerForName">
    <p class="Pname" style="float: left; margin-left: 0px">Name&nbsp;:&nbsp;&nbsp;
        <input class="name" />
    </p>
</div>
<div class="containerForAddress">
    <p class="Pname" style="float: left; margin-left: 0px">Address:&nbsp;&nbsp;
        <input class="adress" />
    </p>
</div><br/>
<div class="containerForCity">
    <p class="Pname" style="float: left; margin-left: 0px">City:&nbsp;&nbsp;
        <input class="city" />
    </p>
</div><br/>
<div class="containerForCars">
    <p class="Pname" style="float: left; margin-left: 0px">Cars:&nbsp;&nbsp;
        <input class="cars" />
    </p>
</div><br/><br/><br/><br/>
<p><font size="3"><b>Source for this<a  target="_blank"href="http://jqfaq.com/how-to-set-focus-on-a-specific-element-after-page-load/"</a> JQFaq question<b/><font/><p/>
<iframe id="iframe1" src="http://jqfaq.com/AdPage.html" style="width:100%; height:115px; border:none;"
/>