Former world No. 2 Tommy Haas won his first singles match since Wimbledon in 2015 on Monday. The German beat Reilly Opelka in the US Men's Clay Court Championship at Houston's River Oaks Country Club.

It was Haas' first win in four events since returning from yet another shoulder surgery. The match featured a large gap in age and experience between 39-year-old Haas and 19-year-old Opelka.

“Happy to have won one again, especially against these young guys who are going to be around for a long time,” he said. “It’s quite interesting to have these matchups.”

Though he’s frequently been injured during his career, Haas has reached the Australian Open semifinals three times, the Wimbledon semis (2009) and an Olympic final (2000). He’s won 15 titles overall.

Now the tournament director of Indian Wells, Haas has still not decided when he will retire.

“I still don't know exactly when that's going to be—the time, which tournament it might be,” he said. “That's not really in my head right now. My main concern right now, still, is to try to get as fit as I possibly can and play, still, at a very high level. At times I feel like I'm still competing and playing at a very high level.

"The consistency is not quite there yet to maybe take it to the next level. But that's the goal—to get to a point where I feel like I'm giving it my very best on and off the court to get to that level again."

Haas is scheduled to play Munich, Stuttgart and Hamburg in the coming months, as well as the three remaining Grand Slams.

He is still eager to get on court.

“I'm looking forward now to the next few months,” he said. “That's what I've kind of had in mind—even at the end of last year, when I was trying to get healthy again—is to play the clay court and grass-court season one more time, and then we'll see what happens after that.”

Haas will play top-seeded Jack Sock in the second round.