Slovakia's Dominika Cibulkova staved off three match points before booking her place in the semi-finals of the WTA Sony Open in Miami with a 3-6 7-6 (7-5) 6-3 win over third seed Agnieszka Radwanska.
With both players struggling in cool, blustery conditions, it was 10th seed Cibulkova who reached the final four for the first time despite being broken 10 times and committing 51 unforced errors and eight double faults.
In an error-strewn contest, Cibulkova had to wait until the fourth game of the second set before managing to hold serve for the first time.
"I have to say I'm really glad, especially about my win today," said Cibulkova, who will move into the top 10 of the world rankings for the first time following the win.
"It wasn't easy at all to play today against Aga with the wind and conditions and I had to stay aggressive all the time even if I missed many shots."
Cibulkova, who took out three-time champion Venus Williams in the fourth round, will play Li Na after she edged out Caroline Wozniacki for a place in the final.
Wozniacki, the 11th seed, looked on course to take the match to a decider after taking a 5-3 lead in the second set, but lost the last four games as Li sealed a 7-5 7-5 success.