Column: Juan Martin del Potro reaches deep inside to advance in U.S. Open

His face was paler than the white stripe on the Argentine flag. Juan Martin del Potro, beset by a fever for two days, looked as if he belonged in bed and not on a tennis court to face No. 6 seed Dominic Thiem in the fourth round of the U.S. Open on Monday night. His performance in the first two sets was ghastlier than his appearance: he won only three games and seemed in danger of collapsing in a sweaty heap at any second.

“I was trying to retire the match in the second set,” he said. “Then I saw the crowd waiting for more tennis.”

What could he do but oblige? Slowly, his fever tamed by medication he had taken during the first set and his spirits buoyed by the many Argentine partisans watching anxiously at the Grandstand court, Del Potro came back to life. The No. 24 seed broke Thiem’s serve early in the third set and perked up, then came back from 2-5 in the fourth set and saved two match points. His forehand, among the best in the game, became a devastating weapon. His pallor and stamina improved.

When it was over, when Thiem double-faulted to seal Del Potro’s thrilling 1-6, 2-6, 6-1, 7-6 (1), 6-4 comeback, Del Potro lifted his arms and thrust his head back, drinking in the love directed his way on a memorable night in Flushing Meadows.

“I couldn’t breathe, I couldn’t move well. Dominic was dominating the match so easy,” Del Potro said. “But then when we start the third set, I broke his serve very quick and then I won the set in 20 minutes. Then the history change a lot.”

It wasn’t that Thiem was lulled into complacency by racing to an early lead or by seeing Del Potro’s sickly state.

“I knew that it’s not going to go all the way like this because if he felt really bad, he would have retired for sure. So I knew I had to be there all the way,” Thiem said. “I knew if he continues to play then he has to feel better or he has to try it. Obviously, set four and five he was playing completely normal.”

Only if normal is defined as wild rallies and edge-of-your-seat drama.

“I took all the energy from the fans. That’s what I did in the end, just keep fighting,” said Del Potro, who moves on to the quarterfinals to face No. 3 seed Roger Federer in a rematch of the 2009 final that produced Del Potro’s lone Grand Slam event title.

In contrast to Del Potro’s exertions, Federer strolled through a 6-4, 6-2, 7-5 fourth-round victory over Philipp Kohlschreiber at Arthur Ashe Stadium. The only excitement occurred when Federer left to get treatment on a tight back muscle but he said he doesn’t consider it a problem.

Federer heard the cheers for Del Potro wafting over from the Grandstand court but didn’t learn the details of Del Potro’s feat until later. Knowing Del Potro’s sad history of wrist injuries, Federer saluted the Argentine’s persistence.

“I’m really happy for him. It’s a good match to look forward to,” Federer said. “Reminds me clearly of the 2009 finals that we had, which was an epic, too. I hope we can produce another good one.”

But he’d prefer a different outcome.

“I felt like that I left that match with a lot of regrets,” Federer said. “Probably feels like one of those matches I would like to play over again.”

Federer stayed on track for a semifinal matchup with No. 1 seed Rafael Nadal, which would be their first meeting at Flushing Meadows. Nadal did his part by easing past Alexandr Dolgopolov 6-2, 6-4, 6-1 for his 50th victory in U.S. Open play.

But before he can renew his splendid rivalry with Federer, Nadal must get past 19-year-old Russian Andrey Rublev, who upset No. 9 David Goffin 7-5, 7-6 (5), 6-3 at Louis Armstrong Stadium to become the youngest U.S. Open quarterfinalist since 18-year-old Andy Roddick in 2001. Rublev, who fired 12 aces and 48 winners while Goffin struggled with a lingering ankle injury, embraced the underdog role against his childhood idol.

“Rafa is the real champion and I’m going to just try and enjoy it,” Rublev said. “This is the quarterfinals. I have nothing to lose.”

Nadal scoffed at that notion, though he likes Rublev enough to have invited the youngster to practice with him on the Spanish island of Mallorca a few years ago.

“This sport is about victory. This is not about defeats,” Nadal said. “No, at the end of your career, nobody remembers your defeats, your losses. People remember the victories.”

Del Potro was exhausted after his magnificent victory and planned to rest Tuesday.

“I know how to play if I want to win, but I will see how physically I feel after this battle,” he said. “But always is a pleasure to play the greatest guy in the history.”

helene.elliott@latimes.com

Follow Helene Elliott on Twitter @helenenothelen