Using jQuery, you could try this:
<script type="text/javascript">
$(document).ready(function() {
var call_ajax = true;
$('#alink').click(function(e) {
if (call_ajax) {
e.preventDefault();
// Do AJAX
call_ajax = false;
}
}
</script>
<a href="http://www.google.com" id="alink">google</a>