NEW YORK -- Andy Murray pumped his fist and then did it again, exulting as if he had just won his match.
Actually, he was still one point away. But considering all the pain Murray has experienced in his hip, sprinting toward the net to chase down a drop volley and put it away was something to celebrate.
Murray and Stan Wawrinka, a pair of former US Open champions, both were winners Monday in their return to the tournament after having to miss it last year.
Wawrinka defeated No. 8 seed Grigor Dimitrov 6-3, 6-2, 7-5, and Murray defeated James Duckworth 6-7 (5), 6-3, 7-5, 6-3.
Both felt good physically, though not quite as good about their chances of contending for the title.
Murray hadn't played in a Grand Slam tournament since Wimbledon last year, before needing hip surgery that has limited him to just eight matches this year. He said before the weekend it wasn't realistic to think he could win this US Open, and the 2012 champion was asked after the match what would have needed to happen for him to change his tune.
"I would have been able to train and practice a lot more than what I have done. I would have played more matches in the buildup to the tournament. I mean, there's many, many things that I would have wanted to change to be considered a contender," he said.
"I don't think anything changes after today. I think I'm still just taking it one match at a time. Yeah, I mean, this is the first time I have played four sets in 14 months, so, you know, I just have to wait and see how I pull up tomorrow."
Wawrinka, the 2016 champion, has a little more reason for hope. He couldn't defend his title last year and needed two left-knee surgeries, but has had some good results this summer. He also eliminated Dimitrov in the first round at Wimbledon, won a couple matches in Toronto before falling to top-ranked Rafael Nadal, and took Roger Federer to three sets in the quarterfinals in Cincinnati.
"I think if you look the last few months, if I separate just my level, just the way I'm playing, the way I'm moving like in [a] practice match or in a match, yeah, for sure my level is really high," Wawrinka said. "I know that, and I'm confident with that."
Murray faces a possible third-round match with 2009 champion Juan Martin del Potro, who's ranked No. 3. He said he'll practice far less now than he used to at Grand Slams, so it's unclear how much better he could get by then. But he improved as Monday went on and said he hopes that continues.
"I made some quite good moves. Like the second-to-the-last point of the match, I moved pretty quickly up to the drop volley and stuff and kind of maintained my serving speeds throughout the match, as well," he said. "So there was some good stuff, but I think I can get better."
Nadal advanced to the second round when David Ferrer retired in the second set of their all-Spanish matchup in Monday's nightcap.
Nadal won the first set but trailed 3-4 in the second when Ferrer had to stop because of injury.
Ferrer said afterward it was his final Grand Slam match and that he was sorry he wasn't able to finish it.
"I'm sad because it's my last Grand Slam. I was enjoying playing the match against Rafa. I was playing good. But anyway, I am proud with myself, with my career,'' said Ferrer, whose best showing at a major was his runner-up finish at the 2013 French Open.
The man who beat him in that title match? Nadal.
"I am 36 years old,'' Ferrer said. "It's time to be home."
He's not quite done with his sport, though. Ferrer, who was ranked as high as No. 3 but is currently 148th, made clear he plans to play a selective schedule of tournaments in 2019.
Still, this felt like a farewell, both to him and to Nadal.
"He deserved a better finish," Nadal said. "I am sad for him."
Also Monday, Kyle Edmund and Roberto Bautista Agut were upset, knocking three seeded men, including Dimitrov, out on the first day of action.
Edmund, the No. 16 seed from Britain, was ousted by Paolo Lorenzi of Italy, 4-6, 6-4, 7-5, 6-1 for a disappointing end to the Grand Slam season after a strong start. He made his deepest run in a major when he reached the Australian Open semifinals in January.
The No. 19 seed, Bautista Agut was swept by Australian Jason Kubler, 6-3, 6-3, 6-4. The Spaniard has grappled with injuries during the second half of the year.
No. 28 seed Denis Shapovalov moved into the second round when his good friend and opponent, Felix Auger-Aliassime, stopped playing during the match between two Canadian teens because he did not feel well.
Shapovalov was leading 7-5, 5-7, 4-1 when Auger-Aliassime retired. Auger-Aliassime already had been visited by a doctor during a changeover in the third set and said his heart was racing.
Shapovalov is 19, making him the youngest player in the ATP top 100.
Auger-Aliassime just turned 18 on Aug. 8, making him youngest player in the ATP top 200. Their combined age made this the youngest US Open men's match since 2006, when Novak Djokovic, 19, beat Donald Young, 17.
Kevin Anderson rallied to outlast Ryan Harrison in five sets to win his first match at the US Open since last year's final.
The No. 5 seed pulled out a 7-6 (4), 5-7, 4-6, 6-3, 6-4 victory in a match that lasted 4 hours, 14 minutes.
Anderson, who fell to Nadal last year in his first Grand Slam final, grabbed at his left calf during the third set but had enough left to win another lengthy match.
The South African won a 26-24 fifth set against John Isner in a Wimbledon semifinal that lasted 6 hours, 36 minutes before losing to Djokovic in the final.
American Jack Sock, seeded 18th, snapped a seven-match losing streak in singles matches on tour with a 6-0, 7-6 (4), 6-2 victory over Guido Andreozzi of Argentina.
It was Sock's first victory in singles since beating Ferrer in Rome in May. He is just 6-15 this year after finishing 2017 with a career-best ranking of No. 8.
It has been a much better year in doubles, where Sock is 26-10 with four titles, including the Wimbledon championship alongside partner Mike Bryan.
The Associated Press contributed to this report.