Iga Swiatek, of Poland, returns a shot to Petra Martic, of Croatia, at the BNP Paribas Open tennis tournament, Oct 8, 2021, in Indian Wells, Calif.  (MARK J. TERRILL / AP)

With world number one and holder Ash Barty sitting out this week's WTA Finals, the only certainty for the eight players competing at the season-ending showdown in Guadalajara, Mexico, is that a new champion will be crowned.

Barty, who counts Wimbledon among the five titles she captured this season, said last month that she would end her 2021 season early due to COVID-19 travel and quarantine restrictions in Australia and start preparing for her home Grand Slam in Melbourne in January.

Her absence means world number four Karolina Pliskova, who is competing in her fifth consecutive WTA Finals, and Spanish No 5 Garbine Muguruza, back for the first time since 2017, are the only two players with previous experience in the event.

Czech Republic's Karolina Pliskova returns against Belarus's Aryna Sabalenka during their women's semi-final match on the tenth day of the 2021 Wimbledon Championships at The All England Tennis Club in Wimbledon, southwest London, on July 8, 2021. (Adrian DENNIS / AFP)

Ash Barty's absence means world number four Karolina Pliskova, who is competing in her fifth consecutive WTA Finals, and Spanish No 5 Garbine Muguruza, back for the first time since 2017, are the only two players with previous experience in the fianls

The rest of the field for the Nov 10-17 WTA Finals will consist of Belarusian Aryna Sabalenka (No 2), Czech Barbora Krejcikova (No 3), Greece's Maria Sakkari (No 6), Estonia's Anett Kontaveit (No 8), Poland's Iga Swiatek (No 9) and Spain's Paula Badosa (No 10).

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Sabalenka will be hoping to put the finishing touches on what has been a breakthrough season that included wins in both Abu Dhabi and Madrid along with semi-final appearances at Wimbledon and the US Open.

Pliskova, widely considered one of the best active players without a Grand Slam title, had a slow start to the season but reached the Wimbledon final before stringing together an impressive run on the North American hardcourts.

Belarus' Aryna Sabalenka poses with her trophy after beating Australia's Ashleigh Barty during their 2021 WTA Tour Madrid Open tennis tournament singles final match at the Caja Magica in Madrid on May 8, 2021. (GABRIEL BOUYS / AFP)

The former world number one finished runner-up in Montreal, made a run to the semis in Cincinnati and then reached the US Open quarter-finals to secure her fifth consecutive spot in the WTA Finals, the longest active qualifying streak on tour.

Muguruza, who won two titles from four finals appearances this season, enjoyed her best WTA Finals showing in her 2015 debut when she lost in the semi-finals to eventual champion Agnieska Radwanska.

READ MORE: Muguruza relieved to end trophy drought with Dubai win

Spain's Garbine Muguruza returns to Tunisia's Ons Jabeur during their women's singles third round match on the fifth day of the 2021 Wimbledon Championships at The All England Tennis Club in Wimbledon, southwest London, on July 2, 2021. (Adrian DENNIS / AFP)

Kontaveit, the final singles player to secure her place in Guadalajara, will bring sky-high confidence into the event given a remarkable end-of-season run during which she came out of nowhere to win 26 of 28 matches and collect four titles.

The eight players will be split into two groups for round-robin play and the top two from each advance to the semi-finals.