Roger Federer defeated Feliciano Lopez with a clinical win on Saturday night (2 September) to erase doubts over his recent performances in the US Open so far.
The 36-year-old returned to action following a past issue which seemed to affect him in his opening two matches as he survived two major scares against Frances Tiafoe and Mikhail Youhzny, with both contests going into the fifth set.
However, Federer showed no signs of any injury as he looked sharper and easily disposed of the Spaniard in straight sets, 6-3, 6-3, 7-5, to progress to the fourth round.
"I'm really excited how I feel after two five-setters," Federer said following the match. "It was clearly nice to go up two sets to love for a change. Feels different from there."
"I needed to get over the fear of the back issue, especially in that first match, the first set. Then I think the wobble I had in the second round was due to my preparation.
"I think now I'm just trusting my movement better. My serve is there. My mind is there. I can finally focus on playing tennis and not so much about the past."
The US Open third seed, who needed just one hour and 46 minutes to defeat Lopez, will now face Germany's Philipp Kohlschreiber in the last 16 as he looks to win a 20th Grand Slam title.
Earlier in the day, world number one Rafael Nadal also progressed to the fourth round with a 6-7, 6-3 6-1, 6-4 win over Argentina's Leonardo Mayer.
Like his win over Taro Daniel, the 15-time Grand Slam winner had to fight back from a set down but eventually took control of the game, dropping just five games from the start of the third set to prevail.
"All the matches have been very tight - I am very happy," Nadal reflected after the game. "I don't know how many break points I had before I got the first one. Mentally, I fought a lot until that moment, then I think I played better."
The Spaniard will face Ukraine's Alexandr Dolgopolov in the fourth round next, who notably knocked out Tomas Berdych in the second round.
A victory over the Dolgopolov followed by a quarter-final win could see Nadal face Federer in the semi-final for the first time ever in the US Open. However, the 31-year-old is not thinking about that possibility.
"I am in the fourth round now. I don't think much about that," he added. "It's a long way away. All the matches have been very tough."
"The only thing I am looking for is the practice tomorrow to keep working hard and focus on the match against Dolgopolov."