World number one Ashleigh Barty was made to battle for a 6-1 7-6 (7) win over Vera Zvonareva and a spot in the second round of the US Open on Tuesday.

The top-seeded Australian came out firing on all cylinders and raced to a 3-0 lead in a rapid-fire opening set that was over in 24 minutes.

But what looked to be a straightforward afternoon for Barty turned tense in a grinding second set which the 36-year-old Zvonareva forced to a tiebreak before falling 9-7.

Barty has won five tournaments this season, including a second career Grand Slam at Wimbledon and her US Open tune-up in Cincinnati.

In between those two victories, however, the 25-year-old endured disappointment when she was knocked out out of the opening round of the Tokyo Olympics by 48th-ranked Sara Sorribes Tormo.

Bencic serving to Netherlands' Arantxa Rus

Elsewhere in the opening round, Belinda Bencic, playing with a new found sense of freedom after winning a gold medal in the singles competition at the Tokyo Games, breezed past Dutchwoman Arantxa Rus 6-4 6-4 to also reach the second round.

Bencic, who reached the US Open semi-finals in 2019 and sat out last year's tournament amid the Covid-19 outbreak, used a solid service game to improve to 3-0 all-time against the left-handed Rus.

Bencic, who is seeded 11th, broke Rus in the first game of the match en route to taking the opening set and again in the second set to go ahead 3-2 before wrapping up the match by forcing a forehand error.

The 24-year-old Swiss, who will face Italy's Martina Trevisan in the second round, said she had been more relaxed on court since her Olympic triumph.

"I kind of achieved my dream in Tokyo. I'm so kind of happy and I'm sure it was my proudest moment which I will ever achieve," said Bencic.

"I feel like it gives me a lot of calmness and just relaxing and I can really play just very free now and I'm playing for fun. "I am feeling good on the court right now so I am not putting any pressure on myself."

World number four Karolina Pliskova fired off eight aces to defeat American wild card Caty McNally 6-3 6-4 in her first-round match as she bids for an elusive maiden major.

Pliskova, the 2016 runner-up, built up a 5-1 lead in the first set before her 19-year-old opponent settled her nerves, and hit 10 winners in the set compared to two from McNally, before breaking the American's serve twice early in the second.

Emma Raducanu celebrating her victory over Stephanie Voegele

McNally, who made it to the third round at Flushing Meadows a year ago, bounced back to level the score at 3-3, with the crowd in Louis Armstrong Stadium cheering her on, but could not match Pliskova's power as the Czech closed out the match with a pair of aces.

She faces Amanda Anisimova in the second round after the American beat Zarina Diyas of Kazakhstan 7-5 6-2.

Emma Raducanu eased into round two with a straight-sets victory over Stefanie Vogele.

The British teenager produced another impressive display at only her second ever Grand Slam, winning 6-2 6-3 to set up a meeting with Zhang Shuai who beat USA's Hailey Baptiste 6-3 6-4.

After making the last-16 at Wimbledon in remarkable fashion, 18-year-old Raducanu triumphed in one hour and 18 minutes at Flushing Meadows.

Sixth seed Bianca Andreescu won in her first match on Arthur Ashe since claiming the title in 2019.

The 21-year-old Canadian seemed to be suffering from stomach cramps in the second set but battled to a 7-5 4-6 7-5 victory over Switzerland's Viktorija Golubic.

Seven seed Iga Swiatek beat Jamie Loeb in straight sets and American Jessica Pegula, the 23rd seed, made the second round with a 6-2 6-2 victory over Anastasia Potapova.