Despite taking the first set, the sixth seed was unable to maintain his advantage, with world No. 56 Atmane recovering for a 4-6, 6-3, 6-4 victory.
The result marked Tiafoe’s first first-round defeat of the 2026 season at his home event in Washington.
Tiafoe, ranked 19th in the world, struggled for consistency throughout the contest, producing 25 unforced errors, including 15 from his backhand. He also surrendered his serve on three occasions and won just 14 of 30 points behind his second delivery.
“My respect to him for winning the match, but very, very poor from my side,” Tiafoe said afterwards.
“I thought I helped him get over the line today, for sure. A lot of mistakes. A lot of easy mistakes, especially on my backhand. Really poor performance in the last two sets from me.
“Very disappointing. Especially for the year that I’ve been having, super disappointing. Honestly, that’s all I can really say. I had a lot of high hopes. Yeah, this one hurts a lot.”
The upset came despite Tiafoe arriving in strong form after capturing the Halle Open, an ATP 500 title, reaching the French Open fourth round and finishing runner-up to Flavio Cobolli at the Mexican Open. It was his 10th appearance in Washington, where he had previously reached at least the quarter-finals four times.
Atmane, who had lost seven of his previous eight Tour-level matches, advances to face Alejandro Tabilo, with second seed Ben Shelton a potential third-round opponent. Tabilo booked his place by defeating Tallon Griekspoor 7-6(3), 4-6, 6-4.
