Los Angeles - Serena Williams was sent crashing out of the WTA Tour's San Jose tournament on Tuesday, losing 12 straight games in a shocking first round defeat to unseeded Johanna Konta.
Williams, who was playing her first match since dropping the Wimbledon final, is trying to regain her top form after missing most of the 2017 season due to a pregnancy.
But the 23-time Grand Slam winner struggled mightily against the British No. 1 and former winner Konta, who crushed Williams 6-1, 6-0 in just 51 minutes on the main Stadium.
"She obviously wasn't playing her best level - nowhere near - so I tried to play the match on my terms and just do what I can out here," Konta said.
Williams, who was seeded sixth, managed just nine winners against 25 unforced errors and had her serve broken six times.
She looked nothing like the player that dominated the Tour for years, winning 72 singles titles and earning more than $86 million in prize money.
Both women were playing their first match since Wimbledon, where Williams finished runner-up to Angelique Kerber and Konta lost in the second round to eventual quarter-finalist Dominika Cibulkova.
The loss comes just over a month after Williams complained that she is being discriminated against by the sport's drug testers because of the number of samples she is being asked to provide.
"Out of all the players it's been proven I’m the one getting tested the most. Discrimination? I think so," Williams wrote in a tweet.
Konta won her maiden WTA title at this event in 2016 when it was held in Stanford University, defeating Serena's older sister Venus in the final.
Konta next faces Sofia Kenin, who earned a dominating win over qualifier Veronica Cepede Royg on Monday.
Konta played a superb match with 17 winners, nine unforced errors and won 83 percent of her first serve points.
This was one of the biggest wins of her career but Konta said she won't be celebrating too long because there is more work to be done.
"I don't believe in big bang moments, or magic moments where the fingers click and it all comes together," she said.
"I believe in continuous hard work and every day perseverance, putting in the work and trusting the process.
"All this match has given me is the chance to play another one. I'm grateful for that opportunity and will work hard for another one."
Results from WTA San Jose tournament on Tuesday (x denotes seed):
Vera Lapko (BLR) bt Zhang Shuai (CHN x7) 7-6 (7/2), 6-0
Timea Babos (HUN x8) bt Kristina Mladenovic (FRA) 6-4, 6-2
Mihaela Buzarnescu (ROU x5) bt Sachia Vickery (USA) 6-3, 4-6, 6-3
Heather Watson (GBR) bt Claire Liu (USA) 6-4, 3-6, 6-4
Johanna Konta (GBR) bt Serena Williams (USA x6) 6-1, 6-0
Amanda Anisimova (USA) bt Wang Qiang (CHN) 6-2, 7-5