Second seed Sloane Stephens was shocked 2-6, 6-4, 6-2 by Germany's Andrea Petkovic in the second round of the Citi Open on Wednesday, disrupting the American's buildup to her U.S. Open title defence.
Stephens' exit left the Citi Open without its two main draws and top seeds after Caroline Wozniacki pulled out of the Washington, DC tournament on Tuesday with a leg injury.
After a straight sets, yet workmanlike victory over compatriot Bethanie Mattek-Sands in her opening match, Stephens had looked poised for another uncomplicated outing as she strolled through the first set.
Yet the world number three ran into considerably more resistance in the second as Petkovic dug in, securing a key break at 5-4 then holding serve to get the match back on level terms.
The 91st-ranked German dictated play in the third set, breaking Stephens twice. She closed out the match with her second break.
Through the first two sets Petkovic faced three break points and could not manage to save a single one, but in the third it was the 30-year-old German applying all the pressure, while not facing a single break point herself.
Petkovic will play the winner of Swiss sixth seed Belinda Bencic's match against Japan's Nao Hibino.
Konta cruises past Kenin in San Jose
A day after handing Serena Williams the worst loss of her career, Britain's Johanna Konta continued her dominance over American competition with a 6-1, 6-4 dismantling of Sofia Kenin at the Silicon Valley Classic.
Konta's service game was once again sharp as she fired nine aces while winning 72 per cent of her first serves and 81 percent of her second against the American teenager on a sun-soaked day at San Jose State University.
Konta, a champion at the tournament two years ago, will face fourth seed Elise Mertens in the quarter-finals after the 22-year-old Belgian cruised to a 6-2, 6-0 win over American Ashley Kratzer.
Earlier in the day top seed Garbine Muguruza withdrew prior to her hotly-anticipated second-round match against former world number one Belarusian Victoria Azarenka due to injury.
"I've been feeling some pain in my right arm for a couple of days and realized I am not ready to play the match," the two-times grand slam champion said.
"Hopefully I can recover for the next tournaments."
Azarenka instead faced tournament lucky loser Anna Blinkova and needed less than an hour to complete a 6-1, 6-0 thrashing of the 19-year-old Russian.
Next up for Azarenka is a quarter-finals showdown against Miami Open semi-finalist Danielle Collins, who dispatched Vera Lapko 6-1, 3-6, 6-1 earlier in the day.
Murray happy to come through hardcourt tests
Former world number one Andy Murray took another big step in his comeback from hip surgery by beating fellow Brit Kyle Edmund 7-6(4), 1-6, 6-4 in the second round of the Citi Open on Wednesday.
The 31-year-old Scot blasted a backhand cross-court return winner on match point to end the two-and-a-half hour contest and dispatch the fourth seed.
Top seed Alexander Zverev won 82 per cent of his first serves in his rain-interrupted match that started on Tuesday against Malek Jaziri en route to a 6-2, 6-1 win over the Tunisian.
Earlier on Wednesday, Nick Kyrgios withdrew from the tournament with a hip injury, another setback in the Australian's buildup to the US Open.
Edmund and Murray were on serve to start the match before trading breaks to set up a first-set tiebreaker, which Murray won when his backhand return caught the line in a call confirmed by video review.
Edmund, who had defeated Murray in straight sets in the second round at Eastbourne in June, fought back in the second set, cutting down on his errors and breaking Murray twice to set up a decider.
Edmund saved two break points at 4-3 to get back on serve but nerves appeared to get to the 23-year-old as sent a forehand long before committing his seventh double fault to bring up match point.
Next up for Murray is a third-round battle with Marius Copil on Thursday. Murray won their only previous meeting last year in straight sets.
Murray, who has added the China Open to his schedule in October as he continues his return from hip surgery earlier this year, said his body was being put through the wringer at the hardcourt tournament.
"I feel better than I did during the grasscourt season, which is positive," said Murray, who played three matches in late June but withdrew from Wimbledon as it came too early in his recovery process.
"So things are still getting better and I've lasted fairly well through two long matches here on a tough surface on the body so hopefully I can keep healing up from the matches and feeling better."
Also in the second round, Denis Shapovalov fired his 15th ace on match point to complete a 3-6, 6-1, 6-4 victory over Russia's Daniil Medvedev.
Medvedev led 4-1 in the third set but 19-year-old Canadian Shapovalov was able to turn it around behind his booming left-handed serve and punishing ground strokes.
Jared Donaldson had to halt the third set of his match against Stefanos Tsitsipas to receive treatment on his right hip and, after failing to convert two match points, fell 3-6, 6-3, 7-5 to the Greek.
There was more injury woe for Australian Kyrgios, who had hurt his hip a week earlier in Atlanta.
The fifth seed made the trip to Washington hoping to be fit, only to pull out of his opening match against compatriot James Duckworth. The world number 17 is scheduled to play tournaments in Toronto and Cincinnati before the U.S. Open, which begins on Aug. 27.
Jason Kubler was awarded Kyrgios's spot in the draw but the lucky loser was unable to take advantage, falling 1-6, 6-2, 7-6(5) to Duckworth.
Americans Frances Tiafoe and Denis Kudla cruised to straight sets wins over Poland's Hubert Hurkacz (6-2, 6-4) and Russian 12th seed Karen Khachanov (6-2, 6-3) while French 14th seed Jeremy Chardy fell 6-4, 6-4 to 93rd ranked Romanian Copil.