In old tennis lingo, an “unseeded floater” was a player who was considered a dangerous opponent if not a contender to win a championship.

At the U.S. Open that starts Monday at the Billie Jean King National Tennis Center, there is just such a floater, one that hovers among the field with a heavy game, one that earned him the 2009 U.S. Open title by beating Rafael Nadal in the semis and Roger Federer in the final.

Welcome back, Juan Martin del Potro.

This is the first U.S. Open that Del Potro has played since 2013. A series of left wrist injuries and surgeries had subverted a career that looked destined for stardom. The 27-year-old Argentine had fallen all the way to No. 1,042 in the world.

But a superlative summer for a player on the brink of losing his livelihood moved Del Potro up to No. 141. He recorded wins over Stan Wawrinka at Wimbledon and an impressive victory over No. 1 Novak Djokovic in the first round of the Rio Olympics. He beat Rafael Nadal in the semifinal before losing to Andy Murray in the final, earning a silver medal and recapturing the attention of the tennis world. The USTA gave him a wild card to get into the Open and Del Potro may well come up trumps.

“I think he is the most dangerous unseeded player,” No. 6 seed Kei Nishikori said. “He has a great chance to win in a Grand Slam. For sure he’s a top-10 player right now. Not going to be easy if you play (him) in the first couple of rounds, but it’s great to see him back on tour.”

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Del Potro’s opening match will be against fellow Argentine Diego Schwartzman Tuesday. Monday’s opening match on Arthur Ashe Stadium will be last year’s beaten women’s finalist Roberta Vinci against Anna-Lena Friedsam, followed by No. 2 seed Angelique Kerber against Polona Hercog and Nadal against Denis Istomin. The night session, which will feature a roof opening and closing, leads with Novak Djokovic against Jerzy Janowicz followed by the American matchup of Madison Keys versus Alison Riske.

There are two first-round matches that pit American veterans against promising young countrymen. Jack Sock takes on Taylor Fritz in the last match on Armstrong Stadium, and John Isner faces Frances Tiafoe in the second match on the new Grandstand Court.

Del Potro, a 6-6 righthander, has a concussive forehand, maybe the biggest in the game. But it was the left wrist, one half of his two-handed backhand, that failed him. He has had three operations on it, causing him to miss two and half years of Grand Slam events, playing 10 matches in 2014 and four in 2015.

Nadal, who also missed more than two months this summer with a wrist problem, realized in Rio that one of the game’s most outstanding players was finally getting back into form.

“He did a good tournament in the Olympics. Happy for him,” Nadal said. “Is tough always the situation that he had through the last couple of years. Del Potro is an important player for the tour and is great to see him back. Is good news for tennis.”

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And bad news for the field.