World number one Iga Swiatek qualified for her ninth WTA Tour of the year, coming from a set down to get past fourth seed Jessica Pegula at the San Diego Open on a rain-affected Saturday.

Swiatek was at her dominant best against Pegula after dropping the opening frame, breaking her opponents' serve four times in the latter two sets to triumph 4-6 6-2 6-2 in two hours and six minutes.

The Pole extended her domination of Pegula this year, winning all four of their encounters in 2022, while the victory is her 63rd of the season, equaling Angelique Kerber's mark from 2016. Swiatek is also 23-1 in the United States this season.

Swiatek finished with 22-8 forehand winners, while she won 75 per cent of her second serves, compared to Pegula's 38 per cent.

After Pegula won the first set that included three breaks of serve, the match was halted for more than an hour due to rain, with Swiatek revealing post-game she passed time with crosswords.

That worked for the top seed who raced to a 3-0 second-set lead after the resumption and did not drop serve for the remainder of the match, saving three break points at 2-2 in the third.

The 2022 French Open and US Open champion will take on either Croatian qualifier Donna Vekic or American world number 19 Danielle Collins in Sunday's decider after their semi-final was ultimately suspended due to rain.

Collins leads Vekic 4-6 6-4 4-2 with the match restarted three times after rain, before the call was made to postpone it until Sunday, no earlier than 12.30pm local time, with the final to be played later in the day.