WHAT HAPPENED: Flamboyant Frenchman Gael Monfils was forced to retire in the third set of his first-round match against Illya Marchenko after landing hard on his right forearm and lower back earlier in the match.

After losing the first set to an in-command Monfils, Marchenko leveled the match in the second set and took control against a clearly hindered Monfils in the third. At 0-5 in the third set – after a lengthy off-court medical timeout and additional on-court timeout to treat his back – Monfils tossed his racquet into the front row of seats behind his chair and offered his hand in resignation.

The No. 16 seed appeared to be in total control of the match against Ukrainian qualifier and world No. 120 Marchenko, winning the opening set 6-2 in 27 minutes of near-faultless tennis.

Two-time US Open quarterfinalist Monfils broke Marchenko in the third and seventh games of the opening set, as nothing the 27-year-old tried appeared to faze Monfils, who was content to run around his backhand and retreat to the back of the court to deal with Marchenko’s softer, looping ball. Monfils dropped just four points on his serve in the opening set, including just one when he got his first serve in play.

The match swung in the Ukrainian’s direction in the middle of the second set when Monfils fell hard on the court. Serving at 1-2 and 30-40, Monfils retreated to play Marchenko’s deep return. As he ran forward four or five steps to play his next shot, he slipped near the baseline. His right ankle rolled under him, and he landed on his right wrist or forehand as an audible gasp went around Louis Armstrong Stadium.

Monfils, who turns 29 on Tuesday, remained on the ground as the chair umpire came down to the court to check on him. To add insult to injury, the point gave Marchenko a much-needed break to go ahead, 3-1.

Marchenko went on to win the set 6-4, as Monfils struggled to regain his form. A pair of exquisite plays at the net – a deft backhand slice volley and smooth shoestring half-volley – were the highlights of Monfils’ post-fall set, which ended abruptly when he sprayed a forehand wide at 30-all and then double faulted to help Marchenko level the match.

Things got worse in the third, as Monfils’ movement appeared even more hindered. He fell behind 3-0 and needed to go off the court for about four minutes to receive medical treatment. After dropping the next two games upon his return to the court, he called the trainer again to work on his back in front of his chair. Monfils came out to serve to stay in the set, but realized he could not continue.

WHAT IT MEANS: Marchenko qualified for the main draw with wins over Hiroki Moriya, David Guez and Adrian Menendez-Maceiras in the US Open Qualifying Tournament last week. The victory puts him into the second round at Flushing Meadows for the second time – he lost to eventual champion Marin Cilic last summer – and helps him improve to 5-10 all-time at Grand Slam tournaments. He’ll face Sergiy Stakhovsky in the second round on Wednesday.

Marchenko’s quarter of the draw is now wide open, with No. 4 seed Kei Nishikori and Monfils – two of the top four seeds in the draw – out of the tournament. That opens things up for No. 19 Jo-Wilfried Tsonga, who would have met Monfils in the third round and Nishikori in the fourth round. No. 7 seed David Ferrer and No. 9 Cilic could benefit from those upsets in the quarterfinals.

QUESTION: Marchenko was 1-4 against Top-50 players entering the US Open, and he had lost five of his past six matches before his victory over Monfils. Stakhovsky, meanwhile, has lost seven of his past eight matches before his four-set win over John Millman on Monday. Can Marchenko ride the momentum of his victory over Monfils to a place in the third round of a major for the first time in his career?