Third-round action got under way on Day 5 of the Australian Open. Here are the key numbers and statistics as the second week of the tournament began to take shape.

Australian Open Day 5

2 - Years since two reigning Grand Slam champions faced off on tour. Roland Garros and US Open winner Iga Swiatek defeated Cristina Bucsa 6-0, 6-1 to set up a fourth-round match against Wimbledon champion Elena Rybakina, who advanced 6-2, 5-7, 6-2 past last year's runner-up Danielle Collins.

The last time two reigning Slam title holders met was in the 2021 Cincinnati quarterfinals, when Wimbledon champion Ashleigh Barty defeated Roland Garros winner Barbora Krejcikova 6-2, 6-4. Swiatek has contested one previous match against a reigning Slam champion while also holding a major title herself -- a 3-6, 6-1, 6-4 loss to Simona Halep in the 2021 Australian Open fourth round.

6 - Points dropped by Swiatek in the first set against Bucsa. The World No.1 won the first 11 games of the match before the Spanish qualifier got on the board.

1 - Zhu Lin's late-night 7-6(3), 1-6, 6-4 upset of No.6 seed Maria Sakkari was the World No.87's first career Top 10 win. Zhu had previously notched two Top 20 victories -- over Petra Kvitova 6-4, 5-7, 6-4 in the first round of Tianjin 2017 and over Elise Mertens 5-7, 6-4, 7-5 in the first round of Dubai 2019.

Zhu had not defeated a Top 50 player during a three-year spell between 2019 and 2022 (partly due to the Covid-19 pandemic). She has notched four in the past four months, over Alizé Cornet in Guadalajara, Katerina Siniakova in the Tampico 125, Jil Teichmann in the second round in Melbourne and now Sakkari. Zhu also defeated former World No.1 Venus Williams in Auckland two weeks ago.

Australian Open: Zhu upsets Sakkari for first Top 10 win

2023 Australian Open

2 - Players who reached the second week of a hard-court major for the first time. Jelena Ostapenko and Elena Rybakina had previously reached at least the quarterfinals of both Roland Garros and Wimbledon but had never made the fourth round of the Australian or US Open until today. Ostapenko had lost in the third round of hard-court Slams six previous times, three apiece in Melbourne and New York; Rybakina had fallen at that stage once at the Australian Open and once at the US Open.

37 - Winners struck by Jelena Ostapenko in 15 games during her 6-3, 6-0 defeat of Kateryna Baindl. Ostapenko had lost all three previous encounters with Baindl, including a 7-5, 6-3 first-round loss at Roland Garros 2018 as the defending champion.

5 - Deuce games won by No.3 seed Jessica Pegula in her 6-0, 6-2 defeat of Marta Kostyuk. Four of the games in the first set went to deuce, with three of those going to multiple deuces; Pegula won all of them.

6 - Zhu Lin is the sixth Chinese woman to reach the second week of the Australian Open in the Open Era, following Li Na, Zheng Jie, Peng Shuai, Zhang Shuai and Wang Qiang.

100 - Jessica Pegula's winning percentage in Grand Slam fourth rounds. The American has won all four she has contested, including two at the Australian Open.

28 - Appearances in a Grand Slam second week for Victoria Azarenka (including 10 at the Australian Open), who notched her fourth win in as many meetings with Madison Keys 1-6, 6-2, 6-1. Azarenka first made the fourth round of a major at the 2007 US Open by upsetting Martina Hingis 3-6, 6-1, 6-0.