Petra Kvitova, who is trying to work her way back into the top three after illness and injury, suffered a blow when the defence of her Dubai Open title lasted no more than one match on Wednesday.
Carla Suarez Navarro of Spain returns the ball to Petra Kvitova of the Czech Repubulic during their tennis match on the third day of the Dubai Duty Free Tennis Championships in Dubai on February 19, 2014
The former world number two from the Czech Republic was beaten by Spain's Carla Suarez Navarro, who spent much of the match trailing but her refusal to give up was rewarded with a 1-6, 6-4, 7-6 (7/4) win and a place in the quarter-finals.
Navarro's consistently heavy ground strokes and superior movement prospered more as the conditions grew slower, and she recovered first from a set and 2-4 down, then from 2-4 down in the deciding tie-break.
Kvitova made one good recovery herself, coming from 2-4 in the final set to lead 5-4 before attempting to close the match out on her serve.
But her flat-hitting game increasingly lacked consistency and gradually the proximity of defeat began to apply its own pressure.
"I started really well, played pretty aggressively, and made a lot of winners, and she didn't have really time to hit well," Kvitova said.
"But when I was leading in the second set, I lost very badly my serve, and I think that from that moment I was like a little bit mentally down."
That may partly have accounted for the two errors she made with her forehand drive, so often her best weapon, which allowed Navarro to come from 2-4 down to 4-4 in the tie-break and which proved the decisive shift of fortunes.
Navarro now plays Alise Cornet, the in-form French number one who followed her conquest of Simona Halep, the seventh seeded Rumanian who won in Qatar last Sunday, by winning 6-3, 6-4 against Kirsten Flipkens.
Another seed to fall was Sara Errani, the fourth-seeded Italian, who lost early in the Middle East for the second successive week, beaten 6-2, 5-7, 6-1 by Sorana Cirstea, the world 27 from Romania.
Earlier on Wednesday Serbia's former world number one Ana Ivanovic claimed that Venus Williams was close to her best again.
The 33-year-old American was certainly impressive in the second round clash which saw her romp to a 6-2, 6-1 victory over Ivanovic and a place in the quarter-finals.
Despite her age, low ranking which sees her outside the world top 40, and repeated health problems, she produced such consistently controlled power that she was unlike the player whom Ivanovic had beaten in the final at Auckland last month.
Her ground strokes were punishing and her serve was consistent, which brought 19 clean winners and five aces in a difficult breeze, but she also had few unforced errors, so often a thermometer of her game.
Asked how close to the best Venus Williams this is, Ivanovic said: "I think it's very close. We played many times in the past. This is her game, you know.
"She was being really aggressive and playing really deep on both wings. I tried even to maybe slice a few, but I just didn't feel like I had too many opportunities."
Williams herself -- who went on to play doubles with her younger sister Serena but lost -- said she had definitely come on from the defeat to Ivanovic earlier in the year.
"I learned a lot from that match," she said.
"I have improved a lot since then, too.
"I have had to take some tough losses, but I have learned from them, and, you know, made them constructive. That's what I'm trying to do each time."
Sister Serena's next match promises to be a high voltage affair as she will face another Serbian former world number one in Jelena Jankovic, who beat the useful Czech Lucie Safarova 7-5, 6-4.
The last meeting between Jankovic and Serena Williams was close and contentious.
It saw Jankovic almost prevent Williams from winning the WTA Championships 2013 year-end title in Istanbul, and later appearing to question her sportsmanship.