Tommy Haas claimed a long-awaited win as defending champion Juan Monaco bowed out of the US Men's Clay Court Championship.
Haas, a former world number two, recorded his first ATP World Tour singles win since 2015 with a 7-6 (7-5) 4-6 6-3 victory over wildcard Reilly Opelka.
The German, 39, only lost four points on serve in the deciding set to edge past Opelka – an American 20 years his junior.
"It's nice to win these matches, especially against the young guys who are going to be around for a long time," Haas said, via ATP.
"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 can recover well and be ready for Wednesday."
Haas, who has undergone nine surgeries throughout his career, faces top seed and 2015 champion Jack Sock in the second round.
Sock also reached the decider last year, but was beaten by Monaco.
A two-time champion in Houston, Monaco fell in the first round on Monday, beaten 7-6 (9-7) 6-3 by Dustin Brown.
Also coming through their opener was Nicolas Kicker, who led Noah Rubin 5-3 when the American qualifier retired with a right wrist injury.