Get what you typing as first result item with jQuery autocomplete?

I try to create a interactive tags field with jQuery autocomplete. But stuck at a functionality that I did not manage to create. What I want to create are:

As soon as you start typing in the tags field, the first item that comes up will be the text you are writing. So when you press enter, that will be selected.

I have attached a image that illustrates this. How do you achieve this?

My code right now:

$(document).ready(function()
{
	$("#filter-field").autocomplete('/search.php',
	{
	width			: 290,
	multiple		: false,
	matchContains	: true,
	formatItem 		: function(data)
					  {
					  return data[0];
					  },
	});
});

From the documentation it has an event called open, in which you could make use of a method that it has to set one of the options.

I can’t get even the simplest “open”-thing to work:

$(document).ready(function()
{
	$("#filter-field").autocomplete('/search.php',
	{
	width			: 290,
	multiple		: true,
	matchContains	: true,
	autoFocus		: false, // The first item will be automatically focused
	formatItem 		: function(data)
					  {
					  return data[0]
					  },
	open 			: function(event, ui) { alert("hej"); }
	});
});

What’s wrong?