Los Angeles - Experience trumped youth on Monday as 39-year-old Tommy Haas defeated 19-year-old Reilly Opelka 7-6 (7/5), 4-6, 6-3 in the first round of the ATP clay court tournament in Houston, Texas.
"It's nice to win these matches, especially against the young guys who are going to be around for a long time," said Germany's Haas, a former world No 2 who is now semi-retired from the tour.
"The nerves when you're trying to win a match are something you can't practice. You can run all day on the treadmill, be in the gym a lot, but you can't substitute that for match play," he added.
"Hopefully I can recover well and be ready for Wednesday."
The ATP said the age disparity between Haas and Opelka was one of the biggest in a tour match in recent years.
In 2011, an 18-year-old Dominic Thiem beat 44-year-old Thomas Muster in Vienna.
Although he's competing in his final season on the ATP tour, and has already turned his attention to pursuits such as serving as tournament director at Indian Wells, Haas said he's not on a nostalgia tour.
He'll be aiming to upset top-seeded American Jack Sock in the second round.
"I don't know any other way, to be honest," Haas said. "If I'm not trying to win the match and play to the best of my ability, then I don't see the point."
Results on Monday in the ATP clay court tournament in Houston, Texas (x-denotes seeded player):
Tommy Haas (GER) bt Reilly Opelka (USA) 7-6 (7/5), 4-6, 6-3
Dustin Brown (GER) bt Juan Monaco (ARG) 7-6 (9/7), 6-3
Nicolas Kicker (ARG) bt Noah Rubin (USA) 5-3 retired