Britain's Emma Raducanu suffered another early exit as she was beaten by Katerina Siniakova in the second round of the Miami Open.
Raducanu served for the match in the third set but ultimately lost 3-6 6-4 7-5 to the erratic Czech.
The US Open champion, 19, has won just two of her seven matches this season.
Earlier, compatriot Heather Watson claimed her first win over a top-20 player since 2020 with a 4-6 6-3 7-6 (7-4) victory over Elina Svitolina.
Watson saved a match point on her way to victory over the 20th-ranked Ukrainian.
It is the first time in six years that Watson has reached the third round in Miami.
Andy Murray begins his campaign later on Thursday against Argentina's Federico Delbonis.
Raducanu, seeded 11th, will be left to rue her missed chances - she converted just five of 17 break points and looked to be affected by nerves as she attempted to serve out the match.
She started the stronger of the two and raced to a 4-1 lead, with a tearful Siniakova taking a medical time-out for what appeared to be a rib problem.
After closing out the first set, Raducanu raced to a break lead in the second before the world number 53 forced a decider.
Raducanu again took a break lead early in the third set and had a chance to go 3-0 up before Siniakova reeled off three games in a row.
Despite this, Raducanu broke and served for the match at 5-4, but a double fault handed the initiative back to Siniakova.
The Czech, ranked number one in women's doubles, was then able to take advantage of a visibly disappointed Raducanu to close out victory.
Watson bounces back for big win
Heather Watson is currently 115 in the world rankingsWatson has dropped out of the top 100 and has opted to miss Britain's Billie Jean King Cup tie with the Czech Republic in April to focus on her singles ranking.
She played well against an out-of-sorts Svitolina and kept her confidence after she let a 4-2 lead slip in the opening set.
She saved a match point as she served to take the deciding set to a tie-break before reeling off three points in a row to claim victory.
Watson will face either 22nd seed Belinda Bencic or Marta Kostyuk next.
Earlier, Naomi Osaka thrashed Angelique Kerber in a meeting of two former world number ones.
Japan's Osaka needed just 60 minutes to beat the 15th-seeded German 6-2 6-3.
The victory is Osaka's first over a top-20 player since last year's Miami Open, when she beat Elise Mertens in the fourth round.
She will face Karolina Muchova next after the Czech beat US Open runner-up Leylah Fernandez 6-4 7-6 (7-3) in their second-round encounter.
Danielle Collins was victorious in her first match since the Australian Open final, where she was runner-up to Ashleigh Barty.
The American came past Hungary's Anna Bondar 6-3 3-6 6-4 to set up a meeting with either Vera Zvonareva or Tamara Zidansek.
Simona Halep withdrew from the tournament before her opening match with a thigh injury.
The Romanian, who reached the semi-finals in Indian Wells last week, said she would be sidelined for three weeks.
Spanish seventh seed Garbine Muguruza also withdrew on Thursday with a shoulder injury.
