The seventh day of the 2021 Australian Open had no shortage of drama when it came to the top players in tennis, who were playing in empty stadiums for the second day due to a snap lockdown in Melbourne after a local COVID-19 outbreak.

Here's what happened:

Naomi Osaka saves two match points to survive

Prior to Sunday, Naomi Osaka had been tearing through the Australian Open draw, winning every set she played by at least three games. That changed against No. 14 seed Garbiñe Muguruza, who pushed the world No. 3 to the brink.

Muguruza opened the match by winning the first set 6-4, the first time Osaka had dropped a set in five matches. Osaka recovered to take the second set 6-4, but fell into deep trouble in the third when Muguruza took a 5-3 lead and went up 40-15 in the next game.

Facing two match points, Osaka came alive. She hit an ace, won a seven-shot rally, then hit a winner to hold serve, and won the next three games to record a furious comeback win, 4-6, 6-4, 7-5. Osaka ended up recording 40 winners and 11 aces.

It was the kind of win that can propel a player to a title, and Osaka reaching the quarterfinals is not insignificant considering she has never not won a tournament after moving past the round of 16.

Up next for Osaka will be Hsieh Su-wei, who will be playing in her first Grand Slam singles quarterfinals at the age of 36. Hsieh's junkballing play style and viral interviews, in addition to upsets over Bianca Andreescu and Marketa Vondrousova, have made her one of the best stories of that tournament, and seeing her against Osaka figures to make for highly entertaining tennis.

Serena Williams fights off Aryna Sabalenka

Just like Osaka, Serena Williams got taken to a third set for the first time of the tournament, but the result was the same: a 6-4, 2-6, 6-4 win.

Facing stiffer competition against world No. 7 Aryna Sabalenka, Williams looked significantly more mobile than she did last year. Poor serving in the second set cost her, but she dug out the win after a 4-4 tie in the third.

If Williams is going to be moving like that and maintaining her dominant serve for the rest of the tournament, odds are good of her finally tying Margaret Court for the most Grand Slam singles titles at 24, on the Australian's home turf.

Williams' campaign will continue in the quarterfinals, against No. 2 seed Simona Halep.

Novak Djokovic overcomes injuries to beat Milos Raonic

An apparent abdominal muscle injury didn't slow Djokovic down on Sunday. Just two days after getting hurt during his Round 3 match against Taylor Fritz, Djokovic bounced back and took down Canada's Raonic, ranked No. 14 in the world. He got a slow start, but got more comfortable as the match went on. He finished 7-6 (4), 4-6, 6-1, 6-4, taking the final sets easily.

He did appear to be struggling slightly, occasionally pulling up short on returns and wincing when he was pulled to the forehand side. But returns like this are why Novak is Novak.

He did admit after the match that he was in a lot of pain and hadn't practiced at all on Saturday.

“[It’s] good enough to compete. It’s not ideal, I’ve felt better," Djokovic said after the match, via Eurosport. "I didn’t have much of a preparation for this match. I didn’t hit a tennis ball since two nights ago.”

Djokovic said that if it wasn't a Grand Slam, he probably would've pulled out by now. Instead, he played and won his 300th Grand Slam match. For his 301st, he'll face No. 6 Alexander Zverev of Germany.

Dominic Thiem shocked in straight sets

The winner of the 2020 US Open officially won't be repeating his hardcourt success down under.

Dominic Thiem, the world No. 3, was shocked in straight sets by No. 18 seed Grigor Dimitrov, losing 6-4, 6-4, 6-0. The match began competitively, highlighted by a 21-point game in which Dimitrov eeked out a break to get back on serve. Thiem wilted as the match went on, though, winning only six points in a 21-minute third set.

Thiem alluded to some issues after the match, but neglected to go into details per the Associated Press. Dimitrov will now advance to face Aslan Karatsev, the unseeded Russian playing in his first ever Grand Slam tournament. If Dimitrov wins, it will be the 29-year-old's first trip to a Grand Slam semifinal, despite being ranked as high as No. 3 in the world earlier in his career.

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