NEW YORK -- Tokyo Olympic champion Alexander Zverev stretched his win streak to 12 matches on Tuesday at the US Open and warned he's aiming to deny top-ranked Novak Djokovic the calendar-year Grand Slam.

Fourth-seeded Zverev, coming off Japan gold and a title two weeks ago at Cincinnati, dispatched American Sam Querrey 6-4, 7-5, 6-2 in a first-round match at Arthur Ashe Stadium.

"I hope in two weeks' time I'll be on an 18-match winning streak," said Zverev, who would claim his first Grand Slam title if he creates such a run.

The 24-year-old German, who lost to Austrian Dominic Thiem in last year's US Open final, hit 18 aces and 40 winners while never facing a break point in advancing after an hour and 40 minutes.

"It's great to be back," Zverev said. "Hopefully I'll play a few more matches here and it will be even more entertaining."

Djokovic, seeking a US Open title to complete the first men's singles Slam since Rod Laver in 1969, opens later against Danish teen qualifier Holger Rume in the night feature at Arthur Ashe Stadium.

The 34-year-old Serbian also seeks his 21st career Grand Slam title, which would break his tie for the all-time record with Roger Federer and Rafael Nadal, both absent due to injuries, as is Thiem.

"Novak is chasing history," Zverev said. "But the young guys are going to try and get in the way of that. I'm going to try to give him a challenge as well."

Zverev, who next faces Spain's Albert Ramos-Vinolas, is a potential semi-final foe for Djokovic and beat him in an Olympic semi-final, rallying from a set and a break down.

"I was also the only person to beat him at a very big event this year," Zverev said. "Everything else he has won. He's the favorite. No question about that.

"I hope I can keep the level up and maybe even play better because to beat Novak here is going to be an extremely difficult task."

Djokovic is unbeaten in 15 US Open first-round matches entering his encounter with 145th-ranked Rune, who has a 13-match win streak in US Open qualifying and Challenger events.

But the 18-year-old is a big underdog to history-chasing Djokovic, who has won eight of the past 12 Grand Slam events.

- Barty, Nishikori win -

World number one Ashleigh Barty, coming off wins at Wimbledon and Cincinnati, began her chase for back-to-back Slam titles by defeating Russian Vera Zvonareva, the 2010 US Open runner-up, 6-1, 7-6 (9/7) in 88 minutes.

The 25-year-old Australian next faces Denmark's Clara Tauson as she goes for her sixth title of the year.

"It has certainly been really enjoyable right from the start," Barty said.

Czech fourth seed Karolina Pliskova, the runner-up to Barty at Wimbledon and the 2016 US Open runner-up, defeating 130th-ranked US teen wildcard Catherine McNally 6-3, 6-4.

"I started really well, lost my focus a little bit at the end of the first set," Pliskova said. "My serve was not really there today. It would be better if I could serve better."

Japan's Kei Nishikori, the 2014 US Open runner-up, eliminated Italy's 113th-ranked Salvatore Caruso 6-1, 6-1, 5-7, 6-3.

Next up for the 56th-ranked Asian star is 61st-ranked American Mackenzie McDonald -- who ousted Belgian 27th seed David Goffin 6-2, 7-5, 6-3 -- with Djokovic a possible third-round opponent.

"I had a great start," Nishikori said. "He really pushed me back and he was playing better. Good to fight through something like this."

Nishikori lost to McDonald in a Washington semi-final four weeks ago.

"I hope I can do revenge," Nishikori said.

Wimbledon runner-up Matteo Berrettini, a US Open semi-finalist two years ago, had a later first-round match against France's Jeremy Chardy. The world number eight from Italy seeks his seventh consecutive victory over Chardy.

Canadian sixth seed Bianca Andreescu plays her first US Open match since winning the 2019 title when she faces Swiss Viktorija Golubic in the final night match on Ashe.

© Agence France-Presse