Roger Federer gave it a valiant run at the 2011 US Open. He played some of the best tennis of the year, but in the end, it ended up serving as yet another reminder that his masterful run of dominance is over.Federer jumped out to a two-sets-to-zero lead over Novak Djokovic. Then Federer was dismantled by Djokovic. Djokovic took the next two sets 6-3, 6-2.Federer regained his form in the fifth and decisive set, and the two went neck and neck, knotted at five. Federer had the serve and was broken. And with that, his tournament was essentially over.Federer went down easy in the last game. And with that loss, I believe we all just saw the end of the great champion contending at a Grand Slam.Federer is facing declining foot speed. It has become increasingly evident as the season has worn on. He just can’t cover as much court as he used to.Federer had used improved first-serve percentage to mask his loss of foot speed at the US Open, but in the end, this wasn’t enough to get him past a top-flight opponent.And while Federer improved his first-serve accuracy, he was not improving it on his ground strokes.Federer’s deft touch meant that in the past it was his opponents who were scrambling while he attacked the court like a surgeon. That is no longer the case.Federer’s lack of foot speed does not allow him to get in position for shots like he used. It is in that split-second where Federer loses his ability to place shots wherever he wants.This is most apparent when he is playing against power players. Federer just can’t catch up to the shots. This is only going to get worse.This is not an attack on Federer. This decline is expected. Federer is 30 years old, and in terms of tennis, he is an old 30. His run of dominance has led to him playing more matches over the past 10 years than any other player. Federer has a had an historically great run, but it is over.