Katie Boulter powers into San Diego semi-finals with straight sets win over Donna Vekic

Katie Boulter is into her first WTA semi-final after beating seventh-seed Donna Vekic 6-3 6-4 at the San Diego Open.

The British No. 1 recovered from a break down in the first set and then again after being broken when serving for the match to set up a last-four clash with either Daria Saville or third seed Emma Navarro as she chases a maiden WTA title.

But it was her quarter-final opponent who started the stronger. Vekic failed to convert a break point to lead 2-0 but made amends on Boulter’s second service game of the match to lead 3-1.

Boulter responded immediately to break back and then fight back from 0-40 to restore parity at 3-3.

Vekic steadied the ship to lead 4-3 before Boulter ran off three consecutive games to clinch a hard-fought opening set that lasted nearly an hour.

And Boulter carried that momentum into the second, storming into a 4-0 lead after breaking twice to make it seven games in a row.

Serving for the match at 5-2, the 27-year-old faltered with the winning line in sight to offer her opponent a lifeline, but she quickly made amends.

After forcing 30-40 on the Vekic serve, Boulter wrapped up a momentous victory at the first time of asking at the end of an epic 24-shot rally.