Latvia's 41st-ranked Anastasija Sevastova handed Serena Williams a shocking first Fed Cup singles loss on Saturday to level the qualifying tie against the USA 2-2 in Seattle.
Sevastova won 7-6 (7/5), 3-6, 7-6 (7/4) to end Williams' perfect Fed Cup record at 14 matches.
The tie will be decided by the doubles late on Saturday night with the winners qualifying for the Fed Cup Finals in Budapest from April 14-19.
"We were playing in the USA so obviously the crowd was going to be for Serena. I just tried to give it my best," Sevastova said of her win at the Angel of the Wings arena.
Williams, the 23-time Grand Slam champion, bounced back from losing the first set by cruising through the second set in 33 minutes, but she was outplayed on the big points for a second tiebreak in the decider.
Sevastova used her powerful serve to deliver aces at key moments, and a precision forehand kept Williams on the move as the American ran out gas in the final moments of the 2hr 25min marathon.
Williams looked fatigued in her first Fed Cup singles match in four years. She had played doubles with sister Venus in her last tournament appearance in 2018.
Williams' loss to Sevastova comes just weeks after she was shocked in the Australian Open last 32 by China's world number 27 Wang Qiang.
Earlier, former French Open champion Jelena Ostapenko had kept Latvia alive with a 6-3, 2-6, 6-2 win over new Australian Open champion Sofia Kenin in just under two hours.
The Americans went into the second day with a 2-0 lead after Kenin on Friday defeated Sevastova and Williams beat Ostapenko to take extend the American great's Fed Cup singles record to 14-0.
"Honestly it's very special to play for my country and I was just trying my best," said Ostapenko, who raced to a 3-0 lead against Kenin and broke her again in the eighth game on the way to winning the first set.
"I was fighting until the last point," she said. "I knew it was going to be a very tough match and the key thing for me was just to play aggressive."
That approach may have contributed to her 49 unforced errors. Kenin made the most of them in the second set, fending off a break point in the first game then pulling away to take a 4-0 lead on the way to forcing a third set.
In a third set that featured six breaks of serve, Ostapenko held for 3-1 and, finally, held in the last game, sealing it on her second match point....