Defending champion Kiki Bertens suffered a surprise 7-6(8), 6-3 loss to world number 50 Maria Sakkari in the third round of the Charleston Open in South Carolina on Thursday.
On a day when top seed Sloane Stephens survived a scare before beating Ajla Tomljanovic 4-6, 6-4, 6-4, Sakkari showcased supreme court coverage skills throughout her almost two-hour match against Bertens.
Sakkari clinched the match after breaking the second-seeded Dutchwoman, who was playing on her preferred clay surface, for the seventh time in the contest.
Sakkari, the 15th seed, saved four set points in the opener and held steady the rest of the way to secure her third career top-10 victory following wins over Caroline Wozniacki in 2017 and Karolina Pliskova last year.
The win also righted the ship for Sakkari, who after a strong start to the year that included a run to the third round at the Australian Open, fell in the early stages of tournaments is St. Petersburg, Acapulco, Indian Wells and Miami.
"I'm pretty excited and speechless," Sakkari said on court.
"I had a rough two months after the Australian Open, I was losing in the first round, second round and I really wanted to come back stronger.
"Finally I came back and I'm feeling great."
Up next for Sakkari will be fifth seed Wozniacki, who beat 12th-seeded Romanian Mihaela Buzarnescu 6-4, 3-6, 6-3.
In the late match, Australian Tomljanovic won the first set with an exquisite backhand drop volley that American Stephens could not retrieve.
Tomljanovic reeled off 13 straight points early in the second set, hitting a series of winners to race to a 3-0 lead, but Stephens wrested back the momentum as quickly as she had lost it.
Croatian-born Tomljanovic continued to go for her shots in the final set but while she hit more winners than her opponent, Stephens prevailed by making fewer errors.
Earlier on Thursday, ninth seed Belinda Bencic extended her fine form with a 6-2, 7-5 win over Taylor Townsend to reach the quarter-finals while Petra Martic beat Jessica Pegula 2-6, 6-3, 6-2.
World No 21 Bencic, who entered the match having lost only six games all week, grabbed eight of the opening nine points to set the tone early.
"The key was to put pressure on her. She's got spin that can make you uncomfortable. If you give her time, she's going to spin you off court and make you run," said Bencic.
"I just tried to play with smart tactics."
World No 1 Osaka signs with Nike
World No 1 Naomi Osaka has agreed a deal with Nike, the sports apparel giant has announced.
The Japanese, who had previously been tied to rival Adidas, will first wear Nike gear at the Stuttgart Grand Prix later this month, the U.S. sportswear maker said on its website.
"I'm proud to become a member of the Nike family and excited about getting involved in all of the opportunities Nike has to offer," said Osaka in the statement.
"Nike has a legendary track record of writing history and I look forward to being a part of those moments for many years to come."
The Japanese has won the last two Grand Slams, having become the first ever Japanese player to win one of the four majors when she overcame Serena Williams at the U.S. Open in September.
"Naomi is an incredible talent to add to our roster and help drive our commitment to inspiring a new generation of female athletes," Nike VP Amy Montagne added in the statement.
"We are thrilled to have her join our team."
Osaka's ascent to the top of the women's game has made her a hot marketable commodity for the world's top brands.
She already has deals with Japanese airline All Nippon Airways, car manufacturer Nissan and watch company Citizen, amongst others.