Top seed Novak Djokovic cannot seem able to get a match in at the US Open, as the world number one was given another rapid advance when Russian Mikhail Youzhny retired due to a leg injury when trailing 4-2 on Friday.
Youzhny was treated during the changeover at 4-1 in the third-round match at Arthur Ashe Stadium and had his left thigh taped. He won the next game on his serve but could not continue, giving Djokovic a pass into the round of 16.
The Serb, winner of this year's Australian Open and French Open to complete a career grand slam, came into the match off a three-day break due to a walkover into the third round when Jiri Vesely of the Czech Republic withdrew.
"It's difficult to pick the words now. I don't think I ever had this kind of situation in my career, where I had a second-round walkover and the third round 30 minutes only," Djokovic said on court before settling in for some practice.
"I'll try to get the positives out of these six games. Obviously I did start very well with a good intensity and I'll try to carry that into the next match."
Defending champion Djokovic will next face either 20th-seeded American John Isner or 84th-ranked Briton Kyle Edmund with a berth in the quarter-finals at stake.
Djokovic, who has been bothered in recent months by a nagging wrist injury, won his opening match at Flushing Meadows on Monday, 6-3 5-7 6-2 6-1 over 247th-ranked Jerzy Janowicz of Poland and is not expected back on court until Sunday.
The 29-year-old Serb was asked whether the long layoff was to his advantage or detriment.
"Depends at how you look at it," he told reporters.
"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.
"From the other side, sure, as you are approaching second week of the grand slam you want to have match play and you want to have time spent on the centre court before you face one of the top players."
On balance, Djokovic seems content with his situation.
"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," he said. "I'm confident that everything is going in the right direction."