Apart from facing three break points in the opening game it was all Williams - 27 winners to just 13 unforced errors, 15 straight points at one point and 18 straight points on serve, fighting off all four of Kvitova's break points - at the end of the day the No.1 seed eased past the No.4 seed in 72 minutes.
Williams now has the standalone second-lonest winning streak in the tournament's history, with 13 wins in a row now - Martina Navratilova holds the record with 21 in a row here from 1983 to 1987.
Williams also kept another streak going - since retiring against Anna Chakvetadze in her first round robin match in 2007, she hasn't lost a set to anyone here other than her sister, Venus Williams (since then she is 5-3 in sets here against her sister and 24-0 in sets here against everyone else combined).
The World No.1 fired 11 aces on Thursday night, improving to 5-0 in her head-to-head with Kvitova.
"I feel pretty good - I was really aggressive tonight," Williams said. "Petra was aggressive too, but I think my serve did really well. I'm just glad to still be alive in the tournament - I didn't have any expectations coming here, I just wanted to come here and enjoy myself, and that's what I've done.
"It just feels good to not be out of the tournament."
Not only is Williams not out of the tournament, she's in fact the only player through to the semifinals so far - with a 3-0 record she will finish first in the Red Group, no matter what happens on Friday.
Kvitova could still qualify for the semifinals - she and Angelique Kerber are both 1-1 in the Red Group, and the two of them will play each other for second place on Friday (read more about that here).
The White Group is more complicated, with three players - Victoria Azarenka, Li Na and Jelena Jankovic - all battling it out for the top two spots. Sara Errani is out of the running in the White Group.
The only match from the White Group on Thursday saw Li beat Jankovic (read more about that here).