US Open final

So I watched a lot of the men's final: Federer vs. Del Potro. Federer did not play his best match. He served poorly, towards the end he mis-hit a lot of balls, it just wasn't one his best efforts. Del Potro played very well, but the thing he did that I think won the match for him seems counter-intuitive.

Federer could have still won the match even playing what was for him, sub-par tennis, except Del Potro somewhere in the third set figured something out that seems to have escaped just about everyone else. What he did, was he slowed his first serve down.

Federer is known as one of the best returners in tennis right now. But this is because he doesn't really do a lot with his return: he typically (especially on first serves), just blocks the ball back in play down the middle of the court.

From his perspective, as long as he doesn't hit the return poorly, he can out-groundstroke just about anyone on the planet. When guys are bombing in 130 mph serves, this is usually enough: just seeing those balls coming back is frusterating enough, knowing that they then will have to trade groundstrokes with arguably the best player in tennis history to win the point is downright disheartening.

Rafael Nadal has long taken advantage of this "weakness" in Federer's game through happenstance: Nadal doesn't use his serve to hurt his oponent, he simply uses it to start the point with the expectation (well deserved) that he will be able to out-groundstroke just about anyone on the planet.

So Del Potro slowed down his first serve because Federer typically doesn't attack first serves. This raised his first serve percentage to well over 70 percent during the last two sets, and got him a lot of balls in the middle of the court so he could dictate the point.

By raising his first serve percentage, Del Potro gave Federer a lot fewer second serves to attack, and in my opinion, this is what won him the match.

Federer in my opinion needs to be just somewhat more aggressive on his return game, both first and second if he is going to beat Del Potro or Nadal consistently in the future.

Unless he just plays out of his mind like he did in the semi against Djokovich.

This is one of the best (and ballsiest) mid-match adjustments I've ever seen at the pro level (especially without a rain delay to permit coaching), and Del Potro richly deserves his win.