US Open 2021: Novak Djokovic, Ashleigh Barty both hold off upset bids

Day 1 of the 2021 US Open had plenty of thrilling wins and dominant performances, but it was short on upsets. Will we see any on Tuesday? Will Day 2 have its own five-set thriller between a high seed and an unranked player?

Check back here for the latest notable happenings from Day 2 of the US Open.

Novak Djokovic drops a set, but holds off 18-year-old Holger Rune

Holger Rune didn't pull off the titanic upset against Novak Djokovic, but a single set should be enough to convince fans he has a future in tennis.

The world No. 1 Djokovic held off the 18-year-old Rune, but needed four sets to do it in a 6-1, 6-7 (7-5), 6-2, 6-1 win. Rune showed plenty of talent in that second set, including a drop shot that made Djokovic look very un-Djokovician.

Alas, Rune visibly struggled with cramping and fatigue starting in the third set, and that's something that just can't happen when you're facing the best player in the world.

Djokovic still had plenty of nice things to say about the Danish youngster though, both to the player himself and in his post-match interview. Djokovic praised Rune's game and said it was "unfortunate" the match had to end the way it did.

The end result was a strong round of applause for Rune as he exited and the continuation for Djokovic's Grand Slam bid. Djokovic will now face Tallon Griekspoor in the second round.

Bianca Andreescu overcomes medical scare in 3-set win

Bianca Andreescu's bid for a second US Open title didn't start easy, but it will still reach the second round.

The tournament's No. 6 seed defeated Switzerland's Viktorija Golubic 7-5, 4-6, 7-5, requiring comebacks in both sets she won and overcoming a brief medical scare in the second set.

Golubic was in position to take the first set just by holding serve, but Andreescu responded with two straight breaks — one of them a 20-point, 15-minute marathon — to take the set. Trouble returned in the second set when Andreescu appeared in tears and required medical attention, but returned to continue the match.

"I just felt I had to throw up. I was super nauseous," Andreescu said after the match. "It was totally fine after a couple games, but it was tough."

The third set was another battle, with Andreescu again falling behind and again battling back. By the time she broke Golubic for the match, after two hours and 49 minutes of play, all she could do was scream:

Andreescu will advance to face Lauren Davis in the tournament's second round,

Pablo Carreño Busta upset after double-faulting match point

As far as US Open choke jobs go, it will be hard to surpass Pablo Carreño Busta.

The tournament's No. 9 seed fell in dramatic fashion to American Maxime Cressy in the first round, despite leading two sets to none and 6-3 in the final tiebreak. On his third match point, Carreño Busta double-faulted to even things up and watched Cressy take the 5-7, 4-6, 6-1, 6-4, 7-6 (9-7) win.

The 24-year-old Cressy entered the US Open ranked 151st in the world, so this would qualify as a massive upset. Carreño Busta reached as far as the semifinals in Flushing Meadows last year and in 2017, but will now head home after one match.

Ashleigh Barty defeats Vera Zvonareva after 2nd-set tiebreak

Ash Barty, back at the US Open after missing the 2020 tournament, is on to Round 2 after defeating Vera Zvonareva 6-1, 7-6 (9).

Barty, who is the No. 1 women's seed at the US Open and ranked No. 1 in the world, came to Flushing Meadows ready to fight. Her attack was sharp and relentless, and showed that she's not taking anything for granted.

She cruised through the first set easily, but began losing ground in the second set almost immediately. Then, with Zvonareva up 3-2, the match came to a standstill for about 7-10 minutes due to a malfunctioning camera. With line calls being decided by cameras instead of line officials, there was no way the match could continue until it was fixed.

Luckily it wasn't a lengthy delay. When play resumed, Barty tied the score back up in a game that took less than two minutes. But Zvonareva kept fighting despite appearing to have trouble with a bandaged thigh. She won three straight games to take the lead at 6-5, only for Barty to tie it up.

The tiebreaker wasn't a cakewalk. Barty wasted at least five match points, but she finally got it done. She survived a torrent of energy from Zvonareva in the second set, and looks primed for a deep run over the next few weeks.

So far on Day 2...

No. 4 seeded Alexander Zverev, who reached the finals last year, took care of American Sam Querrey in straight sets, winning 6-4, 7-5, 6-2. Querrey put up a good fight, keeping Zverev on his toes in the first two sets, but he couldn't manage to get past the world No. 4.

Poland's Iga Swiatek, seeded seventh, rolled over American Jamie Loeb 6-3, 6-4. Loeb literally didn't reach a break point.

The fourth-seeded woman, Karolina Pliskova, beat American Catherine McNally 6-3, 6-4 to advance to Round 2. Belinda Bencic, who recently took home the gold medal in women's singles at the Tokyo Olympics, also beat her opposition in straight sets. Bencic, seeded No. 11, beat Arantxa Rus 6-4, 6-4.

Tenth-seeded Hubert Hurkacz, who knocked Daniil Medvedev out of Wimbledon with a surprise fourth-round win, advanced to Round 2 with a 6-3, 3-4, 6-3 win over Egor Gerasimov.

Maria Sakkari defeated Marta Kostyuk 6-4, 6-3. Sakkari, the No. 17 seed, has had some rough tournaments since she made her first-ever Grand Slam semifinal at the French Open earlier this year, but a first-round win means she won't have a repeat of the Western & Southern Open, where she was eliminated after a first-round loss.