How to watch: 6 p.m. to 9 p.m. Eastern on the Tennis Channel and 9 p.m. to 7 a.m. on ESPN2 in the United States; streaming on the ESPN+ and ESPN3 apps.

Jennifer Brady, the 22nd seed, played college tennis at U.C.L.A. After some initial success on the WTA Tour, reaching the round of 16 at the Australian Open and United States Open in 2017, she struggled for a while. But this past September she broke through with a trip to the semifinals of the U.S. Open after winning her first WTA Title at the Top Seed Open.

Having lost only 11 games across her first three rounds, Brady has shown herself to be a real contender at the Australian Open. Against the 28th seed, Donna Vekic, she’ll need to show the consistency she has used to get here.

Here are some matches to keep an eye on.

Because of the number of matches cycling through courts, the times for individual matchups are at best estimates and are certain to fluctuate based on when earlier play is completed. All times are Eastern.

Rod Laver Arena | 7 p.m. Sunday

Elina Svitolina vs. Jessica Pegula

Elina Svitolina, the fifth seed, reached the quarterfinals of the Australian Open and was the runner-up in the WTA Finals in 2018 and 2019. Remarkably, the defensive baseliner seems to thrive on faster courts, soaking up the pressure from other players and redirecting their pace into clever counterattacks.

Jessica Pegula has had a career delayed by injuries. Now, the 26 year-old has reached the second week of a major tournament for the first time, without dropping a set. In the first round, Pegula upset Victoria Azarenka, the 12th seed and a two time Grand Slam champion. Although that match was perilously close, her second and third round matches were little more than mild inconveniences, as she lost just four games across four sets.

Although Pegula is certainly improving and showing a high level of play, Svitolina will be a tough challenge. Svitolina’s consistency and former experience in the second week of slams will make her the clear favorite.

Margaret Court Arena | 8:30 p.m. Sunday

Mackenzie McDonald vs. Daniil Medvedev

At the 2019 French Open, Mackenzie McDonald tore a hamstring tendon off the bone, leading to a difficult surgery and a lengthy recovery process. Now, he has reached the round of 16, tying his best result from before the injury. McDonald was especially impressive in his second round upset over the 22nd seed, Borna Coric, keeping calm and drawing errors with his consistent, deep shotmaking.

Daniil Medvedev, the fourth seed, struggled in his third round matchup against Filip Krajinovic, losing the third and fourth sets in spectacular fashion. Medvedev cycled between yelling at himself in Russian, his coach in French, and Krajinovic’s well placed volleys in English. In the fifth set, Medvedev settled back in and won six straight games.

For McDonald to pull off an upset, he will need to exploit Medvedev’s natural volatility. Medvedev should be able to keep McDonald at bay if he can keep calm and use his varied shots to pull the American around the edges of the court.

Rod Laver Arena | 11 p.m. Sunday

Rafael Nadal vs. Fabio Fognini

Rafael Nadal, the No. 2 seed, has struggled with a small back injury throughout the first week of the Australian Open. However, this has not stopped him from rolling past his opposition without dropping a set. Nadal’s powerful topspin shots have consistently pushed his opponents around the court, depriving them of the time necessary to impose their own ideas upon a rally.

Fabio Fognini, the 16th seed, has had a roller coaster week. He struggled in a five-set contest against a fellow Italian, Salvatore Caruso, but then dispatched the 21st seed, Alex de Minaur, in just three sets. Fognini, who won a doubles title at the Australian Open in 2015, has been to the round of 16 in Melbourne four times, and will have a difficult time overcoming Nadal.

Rod Laver Arena | 3 a.m. Monday

Ashleigh Barty vs. Shelby Rogers

Ashleigh Barty, the world No. 1, has moved through to the fourth round without dropping a set. In her third round victory over Ekaterina Alexandrova she played smart tennis, not going for big shots and allowing Alexandrova to overplay and extracting 30 unforced errors.

Shelby Rogers, an unseeded player, has reached two major quarterfinals, but has never won a WTA tournament. Her inconsistency on tour can partially be blamed on ruptured cartilage in her knee, which required surgery in 2018.

Barty and Rogers faced off in the quarterfinals of the Yarra Valley Classic last week, with Barty winning in a third-set tiebreaker. For Rogers to reverse her fortunes, she’ll need to play aggressively without over-hitting, a tough needle to thread.

Here are a few more matches to keep an eye on.

Donna Vekic vs. Jennifer Brady — 9 p.m.

Andrey Rublev vs. Casper Ruud — 11:30 p.m.

Elise Mertens vs. Karolina Muchova — 2 a.m.

Stefanos Tsitsipas vs. Matteo Berrettini — 5 a.m.