Harriet Dart and Jodie Burrage both gained excellent victories as the British duo reached the last 16 of the Eastbourne International.
Dart, 26, trailed 3-0 against China's Zhang Shuai but fought back to win 7-5 6-7 (5-7) 6-1 against an opponent 105 places above her in the world rankings.
Burrage, 24, lost the opening set in her match with world number 44 Lauren Davis before winning 4-6 6-4 6-3.
Wimbledon champion Elena Rybakina withdrew from the event though illness.
Dart recovered from a poor start and a mid-match dip in blustery conditions to set up a last-16 tie with either two-time Wimbledon champion Petra Kvitova or former French Open winner Jelena Ostapenko. Kvitova and Ostapenko won titles on Sunday in Berlin and Birmingham, respectively.
"That was a rollercoaster and I'm happy to close it out," said Dart.
"I was not just playing my opponent, but playing myself at times. The conditions were really tough, the wind was going everywhere and it took a while to adapt to it."
Dart, ranked 142nd in the world, reached the quarter-finals of the Nottingham Open and Birmingham Classic earlier this month to get a wildcard for Wimbledon and also for this week's Eastbourne event.
Zhang, ranked 37th, burst into an early lead but Dart won five of the next seven games to reach 5-5, saving three break points in the eighth game.
The decisive break for Dart came in the 11th game before she served out the opening set.
She was twice serving for the second set but had her serve broken at 5-4 and again at 6-5 before losing the tie-break.
Dart received a warning after hitting her racquet on the ground at the end of that tie-break, but quickly regained her composure as she swept through the decisive set.
Earlier this month, Burrage reached the final of the Nottingham Open - her first WTA Tour title match - before losing to fellow Briton Katie Boulter.
British number two Burrage then lost to Dart in the opening round of the Birmingham Classic and on Sunday was beaten 7-5 6-4 in the second round of Eastbourne qualifying by Italian Jasmine Paolini.
However, tournament withdrawals gave Burrage another chance as a lucky loser, and the world number 128 capitalised with a win over qualifier Davis.
Burrage will play another American in the last 16 - either world number seven Coco Gauff or Bernarda Pera.
British number one Boulter faces Croatian lucky loser Petra Martic in their first-round match on Tuesday.
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