Federer cruises while Nadal finds going getting tough
Roger Federer got his US Open campaign back on track but there was another battle for Rafael Nadal as they edged closer to a semi-final meeting. After being taken to five sets in his opening two matches, Federer only needed an hour and 46 minutes to dismiss Feliciano Lopez 6-3 6-3 7-5.
The third seed's movement was much improved and he made far fewer unforced errors as he set up a last-16 clash with German Philipp Kohlschreiber.
Federer said: "I struggled the first couple of rounds, but that had something to do with my opponents as well. I think I played a very clean match tonight, I couldn't be happier.
"To win in straight sets against Feliciano, who's been such a tough competitor over the years, is such a great feeling."
The world number one has looked shaky so far and, after his struggle against Taro Daniel in round two, it was a similar story against lucky loser Leonardo Mayer.
The Argentinian took the opening set on a tie-break and it was not until Nadal finally converted his 14th break point to lead 4-3 in the second that the Spaniard turned on the style.
Nadal won 16 of the final 21 games to clinch a 6-7 (3/7) 6-3 6-1 6-4 victory and a place in the last 16, where he will take on Alexandr Dolgopolov.
The Spaniard, who again was not happy with his forehand, said: "You need matches like this. I am in the second week. That's the important thing. I've already won three matches in a row.
"I think the best thing is I had a lot of moments to be very frustrated in the match, and I was not. I was just fighting for the next point and with the right mentality, with the right spirit of fight in all moments."
Dolgopolov, who beat Viktor Troicki 6-1 6-0 6-4, is one of the more surprising names in the fourth round and the Ukrainian's run comes despite a match-fixing investigation hanging over his head.
Dolgopolov's match against Thiago Monteiro at the Winston-Salem Open attracted suspicious betting pattern.
He was pushed again by the media on Saturday and things became fiery when he was asked whether he had ever been approached to throw a match.
Dolgopolov said: "I already said everything that could be said.
"I'm not going to be talking about gambling. You have other questions or not? We're finished."