Caroline Wozniacki reached the quarter-finals of the Eastbourne International on Wednesday with a 6-7 (3/7), 6-3, 6-1 win over fellow former champion Svetlana Kuznetsova.
But 2014 Wimbledon runner-up Eugenie Bouchard was facing a fitness battle ahead of the third Grand Slam event of the season next week after suffering an event-ending abdominal strain.
The ex-titleholders at Devonshire Park (Wozniacki, 2009 and Kuznetsova, 2004) were meeting for the 10th time, with second seed Wozniacki now leading the series 6-4.
But the Dane lost her way in the opening set as she let a comfortable 5-2 lead slip.
Kuznetsova, a two-time Grand Slam winner, seized the initiative, running off five of six games to force a tiebreak after annulling a Wozniacki set point in the 12th game.
The Russian then prevailed for the early lead after seizing six set points and converting with an ace on her fourth.
“Obviously you’re not too happy with yourself after that,” said Wozniacki.
“But you just have to get yourself together and get back on the horse, as they say, and try to win the second set.
“On grass, losing a set being up 5-1 is not ideal. She started playing better, she started returning deeper and she upped her game. I had a set point I didn’t take.
“Then all of a sudden I see myself being down in the tiebreaker. I don’t know what happened.”
Wozniacki mounted a fightback in the second set and played carefully so as not blow a 5-1 lead in the final set.
“I wanted to make sure that didn’t happen again,” said the former number one, recalling her first-set wobble.
“The only thing that really matters is to get the win.
Wozniacki will play a quarter-final against tenth seed Andrea Petkovic after the German defeated CoCo Vandeweghe 6-3, 6-4.
Belinda Bencic reached her second grass-court quarter-final of the summer, with the Swiss teenager advancing 6-4, 3-0 as Bouchard retired injured.
Bouchard, the seventh-seeded Canadian whose prospects for repeating her Wimbledon final of a year ago are looking exceedingly dim, lasted 54 minutes before calling for the trainer to treat an abdominal injury.
The Canadian could now face a fitness race before the Monday start at the All England Club.
But she vowed: “I’m going to play (Wimbledon) no matter what, even if I’m on one leg. I’ll take a few days off from serving and give it a little break and see how it goes.”
Bencic will now face Britain’s Johanna Konta who put out Spanish 14th seed Garbine Muguruza 6-4, 4-6, 6-3.
Bouchard reached three Grand Slam semi-finals in 2014 but has now lost 11 of her last 13 matches in a slump dating back to mid-March.
Bencic, meanwhile, reached the final on grass in the Netherlands 10 days ago, losing to Camila Giorgi.
She is playing Eastbourne for a second year after losing in the opening round in 2014.
In other results, ninth seed Agnieszka Radwanska beat number eight Karolina Pliskova 6-2, 6-1 and Russian lucky loser Daria Gavrilova defeated Italian 13th seed Sara Errani 6-1, 5-7, 6-2.
Bulgarian Tsvetana Pironkova defeated last year’s Australian Open finalist Dominika Cibulkova 6-7 (4/7), 6-4, 6-1 while American Sloane Stephens knocked out Briton Heather Watson 6-2, 6-3.