Jessica Pegula was at her absolute best as she beat world number one Aryna Sabalenka in straight seta at the WTA Finals in Mexico.

Pegula broke her losing streak against the Belarusian having lost their last five meetings and the American has now won her last five games against top 10 players.

Sabalenka made 33 unforced errors, but it still took Pegula seven match points before clinching a 6-4 6-3 win and a place in the semi-finals.

After the match, Pegula said her improvement comes from feeling "more comfortable" playing top players this year.

Sabalenka will now play Elena Rybakina on Thursday night to determine the second qualifier from the group after Rybakina defeated Maria Sakkari 6-0 6-7 (4) 7-6 (2).

Rybakina started with a fury with a dominant first set but Sakkari fought her way back, winning the second set in a tiebreak.

Sakkari had two break point chances in the final set at 4-4, but Rybakina fought back and finished the tiebreak in a dominant fashion, skipping out to a 6-0 lead.

A number of players, including Sabalenka, Wimbledon champion Marketa Vondrousova and Iga Swiatek criticised the conditions of the courts in Cancun.

For the third year in a row, the host of the prestigious tournament – which features the top eight players of the season – was decided less than two months prior to the event.