US Open 2021: Leylah Fernandez knocks off Naomi Osaka, Carlos Alcaraz upsets No. 3 Stefanos Tsitsipas

Day 4 of the US Open featured domination from the biggest names in the game. Both No. 1 ranked players — Novak Djokovic and Ashleigh Barty — moved on in the tournament. Karolina Pliskova and Iga Swiatek flirted with disaster, but both players pulled out wins in the end.

With all those players getting a day of rest Friday, it will be up to other big names to make the leap into the next round.

Check back here for updates on the notable wins and losses from Day 5 at the US Open.

Leylah Fernandez knocks off Naomi Osaka

Naomi Osaka’s bid to defend her title at the US Open has been cut short.

18-year-old Leylah Fernandez knocked off Osaka on Friday night in a tight two hour battle 7-5, 6-7 (7-2), 6-4 at Arthur Ashe Stadium. The win, by far, marked the biggest of her career — and it will now land her the deepest she’s ever been in a Grand Slam.

The match was a tight one essentially the whole way through, as neither player was able to take more than a two-game lead at any point.

Fernandez rallied back from an early hole to take a 1-0 lead in the first set, and kept moving back and forth with Osaka until she took a 5-4 lead with a dominant ninth game.

That, though, is when Osaka turned it on — rattling off the next three games with ease to close out the set.

Fernandez then jumped up 5-4 once again, before Osaka rattled off a pair of wins to take the lead after breaking Fernandez with a backhand winner in the eleventh game.

Fernandez, though, forced a tiebreak after Osaka made an unforced error and then won the next five points after multiple Osaka errors — something that clearly threw her off her game. At one point she even threw her racquet onto the court out of frustration.

Though she escaped with a single point after Fernandez missed the mark on a return, Fernandez closed out the tiebreaker quickly on two more Osaka errors to take the second set and force a third.

Fernandez kept things rolling into the final set, where she took a quick 3-1 lead and seemed poised to close out Osaka with ease. Fernandez then battled to a 5-4 advantage and won the final game with four quick shots to close out Osaka in just more than two hours and make it into the fourth round of the tournament.

Carlos Alcaraz knocks off No. 3 Tsitsipas

Carlos Alcaraz came up with a massive, historic upset on Friday afternoon at Arthur Ashe Stadium, and he survived yet another Stefanos Tsitsipas bathroom break to pull it off.

Alcaraz knocked off No. 3 Tsitsipas 6-3, 4-6, 7-6 (7-2), 0-6, 7-6 (7-5) in their third round match, which made the 18-year-old the youngest player to defeat a top-3 player in the world at the US Open since 1973.

Tsitsipas, who was slammed after taking a lengthy bathroom break during his first-round win over Andy Murray, stepped away before the fourth set of his match with Alcaraz on Friday. He was down 2-1 at the time, having just lost the third set tiebreaker, but came back and won the next set 6-0.

Though he seemingly retook the momentum, it wasn’t enough. Alcaraz survived a tiebreaker in the final set to take the match and claim the biggest win of his career by far.

Angelique Kerber rallies from slow start to eliminate Sloane Stephens

Friday's match between Sloane Stephens and No. 16 seed Angelique Kerber started out like most of their matchups. Stephens, who had five straight wins over Kerber dating back to 2012, opened the match in full control, taking a 4-1 lead in the first set.

But Kerber rallied to force Stephens to fight for that opening set. And the rest of the match belonged to her as she won the battle of former US Open champions, 5-7, 6-2, 6-3. The loss concludes a return to the spotlight for Stephens, who has struggled to return to form since winning the 20017 US Open. She defeated fellow American Coco Gauff in the second round, sparking hopes of a deep run at Flushing Meadows.

But it was 2016 champion Kerber who survived for a shot at her second US Open title. She did so on short rest after being forced to play her second-round matchup against Anhelina Kalinina on Thursday. She won that match in straight sets after violent weather postponed it from its scheduled time on Wednesday. The three-time Grand Slam champion advances to face the winner between Naomi Osaka and Leylah Fernandez.

Simona Halep survives upset scare against Elena Rybakina

Elena Rybakina pushed Simona Halep to the brink of elimination at the US Open on Friday, but Halep rallied for a late win to remain in the tournament. Halep — ranked No. 12 — needed three sets to defeat the 19th ranked Rybakina to move forward.

Rybakina put pressure on Halep immediately, forcing the first set to go to a tie-breaker. Halep won the tie-break set, giving her a lead going into the second set. Rybakina continued to fight hard in the second set, taking it 6-4.

That set up a critical third set. Halep found herself on the ropes at times during the final set, but eventually recovered to win the set 6-3. With the win, she moved on to the fourth round of the tournament.

Halep's next game will take place Sunday. She will take on the winner of Elina Svitolina and Daria Kasatkina.

Daniil Medvedev moves to fourth round with win over Pablo Andújar

Daniil Medvedev breezed into the fourth round of the US Open with a win over Padlo Andújar on Friday. Medvedev needed only three sets to take down Andújar before advancing.

Medvedev looked dominant from the start, not dropping a single game against Andújar in the first set. Andújar put up a fight in the next two sets, but eventually dropped them 6-4 and 6-3.

With the win, Medvedev will take on the winner of Daniel Evans and Alexei Popyrin on Sunday.

Muguruza tops Azarenka after dropping first set

No. 9 seed Garbiñe Muguruza got an early test from two-time Grand Slam champion Victoria Azarenka. But the Spaniard took control of her third-round match in the second set en route to a 4-6, 6-3, 6-2 win over the 18th-seeded 2007 US Open champion.

Azarenka didn't help herself late, double-faulting on match point to secure Muguruza's win. The two-time Grand Slam champion advances to face Barbora Krejcikova in the Round of 16.

Barbora Krejcikova defeats Kamilla Rakhimova in straight sets

Barbora Krejcikova made quick work of Kamilla Rakhimova on Friday. Krejcikova defeated Rakhimova in straight sets (6-4, 6-2), securing her spot in the fourth round of the US Open.

Through three matches, Krejcivkova has been on her game. She's yet to drop a single set at the US Open. Krejcivkova — ranked No. 8 — will have that streak tested against No. 9 seed Garbiñe Muguruza. The two will meet in the fourth round of the event Sunday.

This story will be updated.