Medvedev, the 2019 champion, came to Ohio looking to get back into shape after his early exit in Montreal, but Lehecka, returning from a back injury that had kept him out of action since Madrid, claimed victory with a 7-6(2), 6-4 win.

Lehecka played with fearless determination and took his chances with 17 forehand winners. The Adelaide champion from earlier this year celebrated his victory by writing a fitting message to the camera after the match: “I’m back!”

The 2022 Next Gen ATP Finals runner-up was out of action for over two months before returning to the court on July 7. Less than a month later, he secured one of the most significant victories of his career.

“To be honest, it’s incredible to be back,” said Lehecka in his on-court interview. “It’s been a long time since I played on a big stage, so I enjoyed every moment today. The fact that such a good and talented player like Daniil wins again is just a bonus for me.”

Lehecka will next face home favorite Frances Tiafoe, who defeated in-form Italian Lorenzo Musetti 6-3, 6-2.

“I served really well today. I was the aggressor, I played pretty deep, very deep,” Tiafoe said in his on-court interview. “But the thing is I just tried to catch him off guard early. He’s played on a lot of different surfaces, he’s played a lot of tennis recently. I know of course he’s trying to do his best at the US Open, but I thought I’ve got to come out really hot and play as fast as I can. I went forward a lot today and I think I really bothered him.”

Greek world number 11 Stefanos Tsitsipas defeated German Jan-Lennard Struff 4-6, 6-4 and 6-3, while world number one Jannik Sinner reached the second round with a 6-4, 7-5 win over American qualifier Alex Michelsen.

The Dane Holger Rune and the Canadian Felix Auger-Aliassime also advanced.