Maybe, just maybe, Novak Djokovic and Roger Federer are feeling some lingering after-effects of their historic Wimbledon final last month.

For Djokovic, it's in the form of a left shoulder that is hurting right now and probably contributed to slower-than-usual serves in the U.S. Open's second round Wednesday night.

For Federer, it's in the form of slow starts: He's lost the opening set each of his first two matches at Flushing Meadows for the first time in 19 times he's entered the Grand Slam tournament.

If they're going to reprise their rivalry late next week in the semifinals, both will need to improve.

Djokovic was repeatedly visited by a trainer for shoulder massages at changeovers during a ragged 6-4, 7-6 (3), 6-1 victory over 56th-ranked Juan Ignacio Londero of Argentina. Djokovic is a righty, of course, but he uses his other hand both for ball tosses on serves and on his two-fisted backhand — and both were less effective for stretches.

"I was definitely tested. This is something I've been carrying for a quite a while now," said Djokovic, who repeatedly shook his left arm between points while serving in his first-round match Monday and did that again this time. "It wasn't easy playing with the pain and you have to fight and hope you get lucky with some shots."

Even though he won for the 35th time in his past 36 Slam matches, including in a fifth-set tiebreaker against Federer at the All England Club on July 14, the Serb looked uncomfortable and went away for stretches, including trailing 3-0 in the second set.

Asked how he plans to prepare for his next match Friday, Djokovic replied with a laugh: "I'll probably freeze my arm for 48 hours, not do anything with it, and then see what happens."

Federer, meanwhile, is not about to start trying new tricks now, despite needing to come back twice already.

He got to the third round by beating Damir Dzumhur 3-6, 6-2, 6-3, 6-4 on an afternoon when rain postponed all but nine scheduled singles matches and every doubles contest.

Still, it's not as if the guy is going to seek some sort of magic solution. Working up more of a sweat in the gym before heading to the court, say. Or playing an extra practice set.

What he chose to focus on, instead, is looking on the bright side: "Can only do better," Federer said, "which is a great thing, moving forward."

At a Flushing Meadows flush with surprises so far — half of the top 12 seeded men already were gone by the time Federer stepped into Arthur Ashe Stadium — he cleaned up his act quickly.

Indeed, Federer was one of the lucky ones who will stay on the usual play-one-day, get-a-day-off Grand Slam schedule. Only matches at Ashe or Louis Armstrong Stadium, the event's two arenas with a retractable roof, were held.

That included a loss by two-time champion Venus Williams to No. 5 seed Elina Svitolina, and victories for No. 2 Ash Barty, No. 3 Karolina Pliskova and 2017 runner-up Madison Keys on the women's side, and a win for No. 7 Kei Nishikori on the men's. In the last matches completed on Day 3, which both ended at around midnight, Serena Williams came back to beat 17-year-old American Caty McNally 5-7, 6-3, 6-1, and qualifier Dominik Koepfer of Germany eliminated Reilly Opelka of the U.S. 6-4, 6-4, 7-6 (2).

"You go through a little phase where you don't start so well and everybody asks you right away, 'What are you going to do?' You're like, I don't know. Just go back to the drawing board. Just do the same things again. You hope for a better outcome," said Federer, owner of a total of 20 major trophies, four ahead of Djokovic. "I don't think there is, per se, a secret to a good start, other than warming up well, being well-prepared mentally, not underestimating your opponent. I did all of that. You know me, I will always do that."

He also ceded the first set to 190th-ranked Sumit Nagal in an eventual four-set victory Monday.

Federer called that pattern "just a bit frustrating, more than anything, especially when the level is that low and there is that many errors and the energy is not kind of there."

Against Dzumhur, who is ranked No. 99 now but has been as high as No. 23, Federer fell behind 4-0 after all of 15 minutes. He was sluggish and his shots were off-target, to the tune of 12 unforced errors within the match's first 19 points.

"Basically," Federer concluded, "the entire set, just sort of donated."

Hardly ideal, on this particular day or in the big picture: Never in the 107-year history of the tournament has a man gone on to claim the trophy after losing the first set in both of his first two matches.

What matters right now, of course, is that Federer is still in the draw.

Borna Coric, who was seeded 12th, was the latest to exit, withdrawing because of a lower back strain before he was supposed to face Grigor Dimitrov on Wednesday. That followed losses Tuesday by a quartet of top-10 men all on Rafael Nadal's half of the bracket: No. 4 Dominic Thiem, No. 8 Stefanos Tsitsipas, No. 9 Karen Khachanov and No. 10 Roberto Bautista Agut.