British number two Heather Watson earned her best win of the year to beat second seed Caroline Wozniacki 7-5 6-4 in the Monterrey Open quarter-finals.
Watson broke the former world number one in the penultimate game of the first set in Mexico and sealed victory when the Dane hit a forehand wide.
The 23-year-old plays France’s Caroline Garcia in Saturday’s semi-final.
Earlier, fellow Britain Johanna Konta lost 6-3 6-7 (2-7) 6-1 to world number 73 Kirsten Flipkens.
Watson has slipped down the rankings to number 70 this year and Saturday’s encounter with Garcia will be her first semi-final since winning the WTA event in Hobart in January 2015.
“I thought I played very well,” said Watson. “I needed to against Caroline because she’s a great player – and I had to fight to the end because I knew she would.”
Konta, ranked 27 in the world, was a set and a break down but broke back to level the second set at 5-5 before winning it in the tie-break.
However, she won only one more game as Belgium’s Flipkens reached the last four.