HOUSTON - In a match representing one of the greatest age disparities on the men's tennis tour in recent decades, 39-year-old Tommy Haas edged 19-year-old Reilly Opelka 7-6 (5), 4-6, 6-3 on Monday at the US Men's Clay Court Championship.

It was the first ATP tour-level victory since Wimbledon in 2015 for Haas, once ranked as high as No 2, but now semiretired and outside the top 800.

Opelka is ranked 168th.

According to the ATP World Tour, Haas is the oldest man to win a tour match since Jimmy Connors was 42 when he reached the quarterfinals at Halle, Germany, in 1995.

"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.

"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.

"Hopefully, I will 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, 18-year-old Dominic Thiem beat 44-year-old Thomas Muster in Vienna.

The tour said the roughly 19.5-year age difference between Haas and Opelka is the fifth-biggest in a tour match since 1995, and the eighth-biggest since 1985.

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 trip.

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."

Haas earned his lone service break against the 6-foot-11 Opelka in the third set. Overall, Haas was 1 for 10 on break chances.

In an evening match, defending champion Juan Monaco bowed out in the first round, losing to the higher-ranked Dustin Brown 7-6 (7), 6-3.

The 124th-ranked Spaniard Monaco won the Houston title in 2012 and 2016. Brown is No 75.

AP - AFP