Five-time US Open champion Roger Federer came out on top in a five-set thriller against Mikhail Youzhny.

The Swiss favorite beat his Russian rival 6-1, 6-7, 4-6, 6-4, 6-2 in a grueling clash, the second five-set victory Federer has had at this year's tournament.

It was the Australian Open and Wimbledon champion's 17th win in 17 matches against Youzhny since their first meeting in 2000 - but both players seemed to struggle for fitness, with Youzhny requiring medical attention in the fourth set.

"It was quite a lot of fun out there. I feel quite warmed up by now," said Federer who fired 63 winners and 68 unforced errors.

"It looked liked Mikhail was cramping at the end and that was hard to watch."

Third seed Federer, 36, will face 35-year-old Feliciano Lopez of Spain for a place in the last 16.

The No. 1 seed, Rafael Nadal, who could meet Federer in the semifinal for their first meeting at Flushing Meadows, had his problems with Japan’s Taro Daniel, going a set and a break down before going on to win 4-6, 6-3, 6-2, 6-2 in two hours and 53 minutes.

"It's true that I didn't play very well tonight but it's also true that I'm through to the next round," said Nadal, a two-time US Open champion Nadal.

There were also wins for Dominic Thiem and David Goffin, sixth and ninth seeds, and Juan Martin del Potro, who glided past Adrian Menendez-Maceiras in straight sets.

Pliskova digs deep

On the women’s side, Karolina Pliskova had to battle back from a set down to make the last 32 and hang on to her world No. 1 spot.

The Czech player, who was runner-up in 2016, downed American qualifier Nicole Gibbs 2-6, 6-3, 6-4.

"It's easier for the other girls to play me as there is more pressure being number one," said Pliskova, who faces either Chinese 27th seed Zhang Shuai or Risa Ozaki of Japan for a place in the last 16.

"Everyone plays their best tennis against me and I felt that today," added Pliskova, who would have lost the top spot in the women's rankings that she has held for just six weeks had she lost.

She was joined in the third round by fourth seed Elina Svitolina, who eased past Russia's Evgeniya Rodina 6-4, 6-4 and French Open champion Jelena Ostapenko, who reached the third round in New York for the first time with a 6-4, 6-4 win against Romania's Sorana Cirstea.