The Pole broke Pegula five times and won the final 11 games in a 59-minute slaughter to capture her first WTA Finals title in a match delayed by a day due to rain.

"I want to thank my team who have been with me for the whole season," Swiatek said during the trophy ceremony.

"We've had many ups and downs but this is for sure an up, and we'll have many more if we keep working like that."

She also thanked the fans that endured countless rain delays and gusting winds over the course of the event at the coastal Mexican resort town.

"Thank you guys for coming and cheering for us, you really made it special," she said.

"Thank you for all these Polish flags and Polish people who are coming to every tournament and those from many countries. Every year I feel like I have more and more support."

Swiatek came into the tournament red hot having won last month's China Open and never dropped a set over the course of her five matches at the event, which brings together the top eight players in the world.

Swiatek ends the season on an 11-match winning streak and will finish the year in the top spot for the second year in a row, having lost the position to Sabalenka after the US Open.

Swiatek, 22, collected six out of her total 17 career titles this season. She retained the French Open crown in June to lift her fourth Grand Slam trophy.

The 29-year-old Pegula, who struggled on her serve and failed to match Swiatek's energy level, was gracious in defeat.

"Congrats on ending the year number one and winning this tournament, it's really incredible" she said.

"You continue to push me to be a better player and I appreciate that aspect of it. I wish I could have done better today but that's not how it goes sometimes."

PLAYERS BLAST WTA

Swiatek's triumph drops the curtain on a WTA Finals where players were vocal in their criticism of their sport's governing body over the slapdash nature of the event.

Cancun was named the venue for the $9 million Finals less than two months before it started and construction of the courts was only completed the weekend before it kicked off on Oct 29.

Sabalenka was particularly outspoken, blasting the WTA over the court conditions after the opening day of group play and saying she felt "disrespected" by the organisation at the prestigious event.

In a letter to the players leaked to the media last week, WTA chief Steve Simon said the late selection of Cancun to host the tournament was "based on a number of complicated factors".

Simon said the WTA accepted responsibility for the poor conditions and signalled changes to the operation of the tour after a series of other complaints from top players about how they are treated.