World number one Angelique Kerber defeated defending champion Heather Watson 6-4, 6-4 to reach the semi-finals of the WTA tournament in Monterrey, Mexico.
Germany's Kerber saved all eight break points she faced in a gritty display against Britain's Watson, setting up a semi-final clash with fourth-seeded Spaniard Carla Suarez Navarro, who was a 6-1, 6-1 winner over French seventh seed Alize Cornet.
"I think it was a good match, especially at the end," said Kerber, who made early breaks in each set stand up despite the pressure applied by Watson.
Three-time champion Anastasia Pavlyuchenkova, the second seed, battled through three sets to defeat fifth-seeded Hungarian Timea Babos 6-2, 3-6, 7-5.
Russia's Pavlyuchenkova needed almost two hours to turn back a late charge from Babos.
She had appeared to be cruising when she took the opening set in less than 20 minutes.
But Babos grabbed a late break in the second set to force the third.
Babos earned the first break of the decisive set, and missed three chances to make it a double break before Pavlyuchenkova broke back to knot the set at 3-3, finally seizing her chance to close out the match on Babos's serve.
"I started to feel the tiredness a little bit - it's been a long and tough trip for me - but I just stayed calm anyhow," said Pavlyuchenkova, who lifted the trophy in Monterrey in 2010, 2011 and 2013.
"I just stayed calm and played every point and fought til the end," added Pavlyuchenkova, who next faces third seeded Caroline Garcia of France. Garcia defeated American Julia Boserup 6-3, 6-2.