All eight ATP round of 16 matches at the US Open were between top-50 players, of whom 15 were seeded. And this round did not disappoint. The favorites may have won most of the matches, but the level of play was very high for most of it.

Honor Roll:
 
Tomas Berdych (defeated Thiem 61 62 64 )- Berdych is very quietly having a strong tournament now. He lost a little focus in his second round against Martin Klizan, and he never found a rhythm against Hewitt in the first round, but he has really played himself into form . His last two matches have featured strong serving, huge hitting, and solid baseline play. He has put himself into position where it should not surprise us if he challenges for the final.
 
Gael Monfils (defeated Dimitrov 75 76 75)- Is Monfils finally ready to take the later stages of Slams seriously? This is not to say that he doesn't care; just that he can sometimes let the showman in him get the better of him at inopportune times. The result of this match can be pinned on Dimitrov, but it was Monfils' grinding defense (and once-in-a-long-while 100-mph forehands) that really won the day. He looks just as strong as anyone remaining in this field. He pushed Federer to the brink two weeks ago in Cincinnati. What can he do this time?
 
Lost Their Homework:
 
Dominic Thiem (lost to Berdych 16 26 46)- Granted, this was Thiem's first second-week appearance at a major, and he looks to have a brilliant career ahead of him. And Berdych made things very uncomfortable for him by pounding the ball all over the court. But Thiem could have done a lot more to keep this interesting. He missed far too many serves and hit too many poor errors. He'll learn from this experience, and he'll be ready to challenge the top players next year, but we were hoping that he could have done more today.
 
Philipp Kohlschreiber (lost to Djokovic 16 57 46)- Djokovic played a very solid match. He didn't go for too much offensively but put in a classic defensive performance that led to many Kohlschreiber errors. Kohlschreiber could never find a way to end points and eventually went for too much. He also made poor deicions at times in this match, losing over 40% of his net approaches. Beating Djokovic would have always been a tough task for the German, but he could have made this a lot closer if he had brought his best game.
 
Jo-Wilfried Tsonga (lost to Murray 57 57 46)- Everything said about Kohlschreiber above can be applied to Tsonga. Murray's defense just forced far too many poor erorrs from the Frenchman. It's a disappointing result for Tsonga, who had to be hoping for more after his performance in Montreal. Murray was playing well, but the Tsonga from three weeks ago could have won this match.

Match of the Round:
 
Is there any other choice? Milos Raonic and Kei Nishikori played an all-time classic late into the night on Monday and into the wee hours of Tuesday morning. The 2:26 AM finish tied for the latest-ever match at the US Open, and this was without any rain delay. These warriors battled for over four hours in the brutal humidity, and the level of tennis never wavered.
 
First of all, we have to stress just how far Raonic's baseline game has come. He is far from the all-serve one-trick pony that he used to be. Nishikori is one of the best power baseliners in the game, and Raonic was able to stick with him in a lot of rallies. Still, the longer rallies went the more likely it was that Nishikori would win them. In an odd reversal of norms, though, Raonic won the first set with a break, and Nishikori took the second in a tiebreak.
 
The third set also went to a tiebreak, which Nishikori should have won. He lost it, though, and all the momentum seemed to be with Raonic. Nishikori was struggling to hold serves to bring the fourth set to a tiebreak, which few had hopes he would win. Nishikori knew better, though, and he took a late break in the fourth set to force a decider. Nishikori took an early break in the fifth set as the match stretched later and later into the night, and he finally served out the match at the incredible hour of 2:26 AM. This was a match that won't soon be forgotten–at least, not by those who stayed up to watch it.