The 2023 champion made a fast start in the Riyadh showpiece, winning 12 of the first 14 points to take a 3-0 lead as a rusty Keys struggled to find rhythm on serve in her first match since a stunning US Open first-round defeat in late August.
Swiatek continued to pile on the pressure on her American opponent, who looked out of sorts in her first appearance in the season finale since her debut in 2016, and the Pole raced away to take the opening set, dropping only one game.
"All the things I practised, I got it together today to play with the right balance, in terms of being solid and aggressive," Swiatek said.
"I'm overall happy with the work that I've put in after the China swing, especially in Warsaw. That gives me confidence, for sure, to go forward and develop as a player."
The pair swapped breaks at the start of the second set, but an untimely double fault from Keys handed the advantage back to Swiatek, who made no mistake from there to wrap up the victory on serve in only 61 minutes.
"I'm happy I could bring my game today," Swiatek added. "I'll be ready to do that (again) in the next days."
The WTA Finals, which features the top eight singles players and doubles teams in the world, has a record prize pool of $15.5 million and offers 1,500 points. The tournament culminates with the finals at King Saud University Sports Arena on November 8th.
Flawless display
In the second match from the Serena Williams Group, former Wimbledon champion Elena Rybakina produced a flawless display on serve to see off WTA Finals American debutante Amanda Anisimova 6-3, 6-1 and get her own campaign off to a winning start.
Kazakh Rybakina, who pulled out of last week's Pan Pacific Open in Tokyo after reaching the semi-finals to qualify for the season finale, showed no signs of the back issue that hampered her to beat Wimbledon and US Open runner-up Anisimova.
"I'm very happy with the way I served," said Rybakina, who dropped only four points on her first serve.
"Amanda's a great player and a tough opponent. I knew I had to serve well... Hopefully I can continue serving like this."
After breezing through the opening set, Rybakina broke early in the next for a 3-0 lead before Anisimova got on the board but there was no stopping the 2022 All England Club champion as she reeled off the games to prevail.
On Sunday, the top-ranked Aryna Sabalenka begins her bid for a maiden WTA Finals title when the Belarusian takes on two-time major finalist Jasmine Paolini of Italy in the Steffi Graf Group before holder Coco Gauff meets fellow American Jessica Pegula.
Unlike in the previous two editions of the tournament, the year-end world number one ranking will not be up for grabs with US Open champion Sabalenka assured of finishing on top after building up a 1,675-point lead over Swiatek heading to Riyadh.
