Thiem downs Dimitrov, Tomic advances

Fourth-seeded Austrian Dominic Thiem won a battle of rising ATP stars, downing Grigor Dimitrov 7-5, 6-2 to reach the semi-finals of the Mexico Open.

Thiem, 22 and ranked a career-high 15th in the world after lifting the trophy in Buenos Aires a fortnight ago and reaching the semi-finals at Rio de Janeiro last week, broke Bulgaria's Dimitrov in the opening game of the second set, and broke again for a 5-2 lead before serving out the win in one hour and 38 minutes.

"Breaking him in the first game of the second set was maybe the deciding moment of this match," Thiem said.

"I started to play better and better and the momentum swung to my side," he said.

Thiem will play American Sam Querrey for a place in the final. Querrey defeated 18-year-old compatriot Taylor Fritz 2-6, 6-4, 6-4.

Friday's other semi-final will pit fifth-seeded Australian Bernard Tomic against Ukrainian Alexandr Dolgopolov.

Tomic, playing his fourth quarter-final of the year, edged Ukraine's Illya Marchenko 7-5, 7-5 while Dolgopolov cruised past Robin Haase of the Netherlands 6-3, 6-3.

Tomic, ranked 21st in the world, broke Marchenko five times.

Dolgopolov, coming off an upset of top seed and defending champion David Ferrer of Spain, needed just 64 minutes to subdue Haase and said he'd try to maintain his aggressive mindset against Tomic.

"We've played a lot of times," said Dolgopolov, who has won six of nine career meetings with Tomic. "He's a tricky player. He slices well, he plays all around the court, serves well and breaks up your rhythm. I think it will be on my racquet because I risk a bit more than him in general."

In women's action, second seeded American Sloane Stephens defeated Japanese wild card Naomi Osaka 6-3, 7-5 to set up a semi-final clash with eighth-seeded Belgian Yanina Wickmayer, who upset third-seeded Russian Anastasia Pavlyuchenkova 6-3, 7-6 (7/3).

Slovakia's Dominika Cibulkova -- who reached the quarters on a walkover when top-seeded Victoria Azarenka pulled out with a left wrist injury -- advanced to the semis with a 3-6, 6-2, 6-3 win over sixth-seeded Swede Johanna Larsson.

Cibulkova next faces American Christina McHale, who defeated Croatian Mirjana Lucic-Baroni 6-4, 6-7 (7/9), 6-2.