World No. 1 Naomi Osaka succumbed to a straight-sets defeat to Yulia Putintseva at the Birmingham Classic on Thursday, handing Ashleigh Barty the chance to end the week on top of the rankings.
Osaka admitted ahead of her first grass court tournament of the season that she is still not at home on the surface and it showed as Putintseva romped to a 6-2, 6-3 win.
The US and Australian Open champion now runs the risk of heading into Wimbledon short of match practice on the grass as she has not signed up to play in Eastbourne next week.
Putintseva made a blistering start to go 5-0 up in the first set and Osaka's troubles on serve throughout the match ensured she never recovered.
Osaka dropped serve at the start of the second set. She fought back to lead 3-2 before Putintseva won the last four games to close out the match in a little over an hour.
French Open champion Barty can secure World No. 1 by winning the title in Birmingham and she eased into the quarterfinals with a 6-3 6-1 victory over Jennifer Brady.
Only the rain threatened to slow Barty as it delayed the start of the match and then briefly interrupted the second set.
However, Barty was too focused and too good for Brady and made it nine wins in a row after claiming her maiden Grand Slam title in Paris earlier this month.
Barty could face five-time Wimbledon champion Venus Williams in the last eight on Friday should the 39-year-old see off sixth seed Wang Qiang of China.
Bautista Agut advances
In the ATP 500 tournament in Halle on Wednesday, Spain's Roberto Bautista Agut beat France's Richard Gasquet in straight sets.
Seventh seed Bautista Agut, who reached the semifinals in Halle last year before pulling out with injury, sauntered to a 6-1, 6-4 second-round victory over Gasquet on Thursday.
The Spaniard joins Matteo Berrettini and Alexander Zverev in the quarterfinals, both of whom also won their second round games.
Important results: ATP 500 tournament, Halle: Second round: Alexander Zverev bt Steve Johnson 6-3, 7-5; Roberto Bautista Agut bt Richard Gasquet 6-1, 6-4; Matteo Berrettini bt Andreas Seppi 4-6, 6-3, 6-2.
Borna Coric bt Joao Sousa 7-6(4), 5-7, 7-6(4); Pierre-Hugues Herbert bt Sergiy Stakhovsky 2-6, 7-6(2), 6-4.
ATP Queen's Club: First round: Jeremy Chardy bt Mikhail Kukushkin 6-1, 6-3; Juan Martin del Potro bt Denis Shapovalov 7-5, 6-4; Milos Raonic bt Marco Cecchinato 6-3, 6-2; Stanislas Wawrinka bt Daniel Evans 6-3, 6-4.
WTA tournament, Mallorca: Second round: Elise Mertens bt Samantha Stosur 6-3, 6-3.
Birmingham Classic: Second round: Yulia Putintseva bt Naomi Osaka 6-2, 6-3; Jelena Ostapenko bt Johanna Konta 6-3, 6-4; Barbora Strycova bt Su-Wei Hsieh 7-6(3), 6-3; Kristyna Pliskova bt Karolina Pliskova 6-2, 3-6, 7-6(7).
First round: Venus Williams bt Aliaksandra Sasnovich 6-3, 6-4; Ashleigh Barty bt Donna Vekic 6-3, 6-4.