Ana Ivanovic claimed a second stunning victory in two days as she overcame top seed and defending champion Simona Halep 7-6 (2) 6-2 to reach the quarter-finals of the Dubai Duty Free Tennis Championships.
Second seed Garbine Muguruza also made an early exit as she was beaten 7-6(3) 6-3 by Elina Svitolina, who has former world number one and four-time Dubai champion Justine Henin as part of her coaching team.
Caroline Garcia defeated third seed Carla Suarez Navarro 4-6 6-4 6-3, and fourth seed and former Dubai champion Petra Kvitova was beaten 0-6 7-6(1) 6-3 by Madison Brengle.
Ivanovic's coach Nigel Sears had to convince the Serb to ignore distractions from water leaking onto the court and concentrate on her game.
The strategy worked, with Ivanovic saving a set point before taking the opening stanza in a tiebreaker.
The second began with a run of consecutive breaks before Ivanovic took command to reach 5-2, closing out victory a game later.
Ivanovic next plays Czech Barbora Strycova, a winner over German Julia Goerges 2-6, 6-3, 6-1.
World number 17 Ivanovic called her win over Halep "one of the highest quality matches I have had in maybe the last year".
"I started a little bit anxiously. I was rushing too much. But I was really happy I managed to calm down and raise my level and win," she added.
Romanian Halep was just pleased to be feeling close to full fitness having been plagued by a nasal infection recently.
"I was doing OK, I was aggressive. She played really well. She came back well," Halep said.
"I'm disappointed that I lost but it's OK. I feel good. I have no pain anywhere. It's good, and the most important thing is that I'm healthy."
Elina Svitolina, whose new coaching advisor Justine Henin was in the stands, beat a tearful Muguruza, 7-6 (7-3), 6-3.
Muguruza, the 2015 Wimbledon finalist, struck 68 unforced errors in her loss to the Ukrainian.
"I'm not really finding my game," the world number five said. "I'm not really ready to compete. I need to work a little bit more."
Caroline Garcia of France waited out a rare rain interruption before advancing to the quarters with a 4-6, 6-4, 6-3 win over Suarez Navarro.
The two players were forced off court until evening due to rain, which only hits Dubai a few times a year.
The weather arrived with the Frenchwoman leading 5-3 in the decider, but she served it out on the resumption to complete the win.
American Madison Brengle shocked double Wimbledon winner Kvitova 0-6, 7-6 (7/1), 6-3 in a contest which ended early Thursday morning.
Wimbledon finalist Muguruza is struggling at the moment and may take a short break from the game to re-group after a disappointing start to the year.
“I'm not really finding my game, so I think I have to rest a little bit and concentrate again and work hard and eventually come back to the tournament to play again,” said Muguruza.
“I think I'm not really ready to compete. I need to work a little bit more. My shots, my fitness. So we'll see. I think I just need to start from zero again and kind of forget these couple of tournaments, I guess.”
The Dubai Duty Free Tennis Championships is owned and organised by Dubai Duty Free, and held under the patronage of His Highness Sheikh Mohammed bin Rashid Al Maktoum, Vice-President and Prime Minister of the UAE and Ruler of Dubai.