World number one Iga Swiatek of Poland rallied after a rain delay to defeat sixth-ranked American Jessica Pegula on Saturday and reach the WTA San Diego Open final.

Swiatek, seeking her eighth title of the year, advanced to her ninth WTA final of the season by defeating Pegula 4-6, 6-2, 6-2 after two hours and six minutes.

But the three-time Grand Slam champion will have to wait until to find out her opponent in the championship match.

Heavy rain forced suspension of the second semi-final with 19th-ranked American Danielle Collins, this year's Australian Open runner-up, leading Croatia's 77th-ranked Donna Vekic 4-6, 6-4, 4-2, after two hours and 29 minutes.

In a rematch of this year's French and US Open quarter-finals, Swiatek dropped the first set just before a lengthy rain delay that allowed the 21-year-old Polish star to regroup.

"I came back and I wanted to be really composed and not lose in those important moments," Swiatek said.

Swiatek raced ahead 3-0 and broke again on a forehand winner in the eighth game to force a third set, which she also dominated, taking the victory with a break when Pegula netted a forehand.

Winner of a WTA-best 63 matches this year, Swiatek improved to 4-1 all-time against Pegula, having lost their first meeting in 2019 at Washington but wining this year at Miami and in the US and French Open quarter-finals.

Swiatek, a runner-up last week at Ostrava, seeks her 11th career WTA title. Her titles this year include Qatar, Indian Wells, Miami, Rome, Stuttgart and the US and French Opens.

Collins won her only WTA titles last year at Palermo and Silicon Valley.

Vekic won her third career WTA title last October at Courmayeur in her most recent tour final.