World number one 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 number one by winning the title in Birmingham and she eased into the quarter-finals 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.