Los Angeles - Bethanie Mattek-Sands, playing her first WTA singles match since the Australian Open, rallied to beat Venus Williams 6-7 (4/7), 6-3, 6-1 on Tuesday in the hardcourt tennis tournament in San Jose, California.
Mattek-Sands, 34, notched her first singles match win in more than a year - since a first-round victory at the 2018 French Open.
She dropped her serve to open the third set, but won the final six games to set up a second-round clash with Spain's eighth-seeded Carla Suarez Navarro.
"I'm in for another match, so I'm pumped," said Mattek-Sands, who like seven-time Grand Slam champion Williams received a wild card into the draw.
Mattek-Sands was sidelined for more than a year after suffering a ruptured Patella tendon and dislocated kneecap at Wimbledon in 2017.
She returned to win the US Open mixed doubles title in 2018, but has been sidelined again this year by another knee injury.
"It's been a tough couple of years," she said. "I've had a few surgeries - I feel like I've had 12 surgeries - but I'm feeling really good."
Unable to capitalise in the first-set tiebreaker after clawing back from 4-2 down, she dominated the next two sets.
"I think I neutralized Venus's serve a little bit," Mattek-Sands said. "A lot of times she can get some free points on that first serve, so I stood back a little bit."
In other first-round action, former world number one Victoria Azarenka of Belarus overpowered French qualifier Harmony Tan 6-2 6-4.
Azarenka converted seven of her 12 break point chances to line up a meeting with fifth-seeded Donna Vekic of Croatia, a 6-4, 3-6, 6-4 winner over Japan's Misaki Doi.
Results on Tuesday in the WTA tournament in San Jose, California (x-denotes seeding):
Zheng Saisai (CHN) bt Heather Watson (GBR) 6-3, 6-1
Danielle Collins (USA x8) bt Zhang Shuai (CHN) 6-4, 5-7, 6-2
Donna Vekic (CRO x5) bt Misaki Doi (JPN) 6-4, 3-6, 6-4
Victoria Azarenka (BLR) bt Harmony Tan (FRA) 6-2, 6-4
Madison Brengle (USA) bt Andrea Petkovic (GER) 6-0, 6-3
Bethanie Mattek-Sands (USA) bt Venus Williams (USA) 6-7 (4/7), 6-3, 6-1