WTA Finals: Jessica Pegula advances to semi-finals after shock win over Aryna Sabalenka

Jessica Pegula is the first player to advance to the WTA Finals semi-finals after the American upset world No 1 Aryna Sabalenka to win her second group stage match in Cancun on Tuesday evening.

Pegula, who entered the contest with a 1-4 record against Australian Open champion Sabalenka, managed to absorb her powerful serve to extend rallies and thwart the Belarusian's comeback attempts in a 6-4, 6-3 victory.

Sabalenka, who has heavily criticised the organisers and complained about the quickly constructed court, never looked totally comfortable against Pegula, committing 29 unforced errors on a sunny day in the coastal Mexican city.

The top seed appeared on the comeback march in the first set when, trailing 5-2, she pounded a thunderous forehand winner to break Pegula and backed that up with a service hold to pull within a game of the American.

But Pegula kept her cool and captured the first set after a tense rally ended with a backhand into the net by Sabalenka on set point.

Pegula raced out to a 4-0 lead in the second set, but Sabalenka once again rallied, breaking serve to cut Pegula's lead to 5-3.

It took seven match points in the marathon final game of the match for Pegula to finally deliver the knockout punch, which came when Sabalenka shanked a backhand to deliver Pegula her fifth straight win over a top-10 opponent.

After the match, Pegula pushed back on the notion that her game is lacking in power compared to the likes of Sabalenka.

"I hit hard," she told Tennis Channel. "People don't seem to think I hit hard, like commentators. Seriously, I don't know why they say that. Maybe because it looks like I'm not? I hit flatter, I don't hit as heavy as maybe as Aryna, but I hit hard."

Pegula's second group stage win in