Top seed Simona Halep has battled past German Julia Goerges 7-6(1) 7-6(6) to set up a semi-final clash with Ukrainian Elina Svitolina at the Qatar Open.
Playing in her first tournament with new coach Thierry Van Cleemput, Halep raced to a 4-0 lead in the opening set before her ninth-seeded opponent fought back to force a tiebreak.
Goerges threatened with an early break in the second set but Halep's relentless accuracy from the baseline proved the difference as the Romanian closed out the win in just over two hours on Thursday.
Fourth seed Svitolina swept aside Czech qualifier Karolina Muchova 6-4 6-2 to move into her first semi-final of the season.
Svitolina broke her opponent twice in each set, winning 78 per cent of points on first serve.
Muchova, who has enjoyed a breakthrough week to reach her first WTA quarter-final, was undone by 25 unforced errors, allowing Svitolina to clinch an 82-minute victory.
"She's not as a typical young player because most of the players now that are coming up are smashing the ball," Svitolina said.
"She has lots of variety in her game, and that's, I think, very good for tennis."
Three-time grand slam winner Angelique Kerber rallied from a set down to overcome Czech Barbora Strycova 1-6 6-2 7-6(4), reaching her first semi-final since her Wimbledon triumph in July.
Kerber's Australian Open campaign in January ended in one of the worst defeats of her career when she won only two games against Danielle Collins but has put it behind her in Doha.
Both players converted five break points in a riveting contest but it was Kerber who kept her composure in the decisive tiebreak to improve her head-to-head record to 8-1 against Strycova.
