Novak Djokovic looks to take another step towards a third US Open title when he faces British outsider Kyle Edmund for a place in the quarter-finals on Sunday, dismissing fears of ring-rustiness after two free passes in the first week.
The world number one needed four tough sets to beat Jerzy Janowicz in the first round last Monday.
But he skipped the second round when Jiri Vesely handed him a walkover with an arm injury before Mikhail Youzhny lasted just six games and 32 minutes before calling it quits with a hamstring injury in Friday's third round.
World number 84 Edmund, by contrast, is battle-hardened having defeated top 20 seeds Richard Gasquet and John Isner to make the last 16 for the first time.
"Considering the stage of the season, the amount of matches I've played, what I've been through with my body, I think it's actually good to have some days off and then shorter matches," said Djokovic, chasing a third major of 2016.
"But, again, I'm not too concerned about my game itself. I've worked hard last couple days. Health-wise I feel much better than I did at the beginning of the tournament. I'm confident that everything is going in the right direction."
Edmund, 21, was one of three British men to make the third round -- the first time that there have been so many at that stage in New York since 1968.
Edmund said he hopes to take positives from his only previous meeting with the Serb, a 6-3, 6-3 loss in Miami this year.
"He's obviously a great player. He's tough to break down. Makes a lot of balls. Very quick around the court. He has lots of good abilities. He's world No. 1. He's good in all areas," said the Johannesburg-born Briton.
Fellow two-time champion Rafael Nadal also chases a quarter-final spot on Arthur Ashe Stadium on Sunday. The fourth seed tackles French 24th seed Lucas Pouille.
Nadal beat Pouille comfortably in their only other previous meeting in Monte Carlo last year where he gave up just three games.
Nadal has been impressive in New York and has shown few signs of the wrist problems which sidelined him from midway through the French Open until the Olympics.
Sunday's other fourth round ties feature two other Frenchmen.
Ninth seeded Jo-Wilfried Tsonga faces America's Jack Sock, who beat 2014 champion Marin Cilic, while Gael Monfils takes on Cypriot veteran Marcos Baghdatis.
The bottom half of the women's last 16 will be played out with second seeded Australian Open champion Angelique Kerber facing two-time Wimbledon winner Petra Kvitova.
In the battle of left-handers, the two are tied at 4-4 but have never met at a Grand Slam.
Kerber has won the last two -- at the WTA Championships at the end of 2015 and in Stuttgart on clay on the eve of the French Open.
US eighth seed Madison Keys faces two-time runner-up and former world number one Caroline Wozniacki.
Fourth-round first-timer Anastasija Sevastova, who put out French Open champion Garbine Muguruza in the second round, meets British 13th seed Johanna Konta.
Fellow debutant Lesia Tsurenko of the Ukraine faces 2015 runner-up Roberta Vinci of Italy.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)