In Tuesday’s earlier match, Wimbledon champion Krejcikova faced little challenge from a below-par Pegula, who last year reached the tournament’s final.
In a performance devoid of any positive energy, Pegula struggled to cope with the Czech’s huge serves, including 11 aces, and hit just four winners in a match lasting little more than an hour.
US Open finalist Pegula, 30, had got off to the perfect start with a love hold in her first service game, amid a catalogue of Krejcikova unforced errors.
But after Krejcikova got the initial break midway through the first set, sixth seed Pegula’s body language began to sour and she gifted her opponent the opener with a sloppy return tapped into the net from close range.
Form did not improve for Pegula at the start of the second set as Krejcikova broke her serve at the first opportunity, though there was a brief reprieve for the American as she cancelled that out in the next game.
But any glimmer of hope for a Pegula comeback was extinguished as she double-faulted to give her opponent the break back, after which Krejcikova – whose performance was far from polished – coasted to a straightforward victory with a solitary break point her only hurdle.
“I’m really pleased with the way I played today. I felt I had to play my best tennis,” said eighth seed Krejcikova, who is ranked 13th in the world but qualified for the WTA Finals on account of being a 2024 Grand Slam champion.
“I had some very high parts of the season, especially winning the Wimbledon title. It was something that is really indescribable, and to be here right now is a huge privilege to be playing in the final eight.”
The WTA Finals are being held in Saudi Arabia for the first time – a move which has been criticised by some because of the country’s human rights record.
This year’s tournament has record prize money, with the singles champion set to collect about £4m.
In Wednesday’s final Purple Group round-robin matches, Sabalenka will take on Rybakina before Jasmine Paolini and Zheng Qinwen go head-to-head for a place in the semi-finals.
