Did you even see the 2nd exhibition match? If you did, you would have seen Federer hitting to Sampras' backhand most of the time during baseline rallies in order to deny Sampras his famous running forehand. Sampras was joking and clowning around with Federer, the crowd, the linespeople, etc., while Federer was all business. Federer only smiled when Sampras did something funny but he never initiated anything funny himself. He was focused and serious. It was easy to tell.