The 2023 champion made a fast start in the season-ending championships showpiece in Riyadh, 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 shock 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.
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.
The WTA Finals, which features the top eight singles players and doubles teams in the world, culminates with the finals at King Saud University Sports Arena on Saturday November 8.
In the second match from the Serena Williams Group on Saturday, former Wimbledon champion Elena Rybakina beat Amanda Anisimova, of the United States and runner-up at both Wimbledon and the US Open this year, 6-3 6-1.
On Sunday, the top-ranked Aryna Sabalenka begins her bid for a maiden WTA Finals title when she takes on 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 No.1 ranking will not be up for grabs as US Open champion Sabalenka is assured of finishing top.
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