NEW YORK (AFP) — Serena Williams delayed her farewell to tennis on an electrifying opening night at the US Open on Monday as the sporting icon battled to victory in front of a star-studded crowd.

The 23-time Grand Slam winner — who earlier this month signaled she plans to retire from tennis after the tournament — drew on all of her experience to down lowly ranked Montenegrin opponent Danka Kovinic 6-3, 6-3.

A galaxy of celebrities ranging from Hollywood stars, fashion icons and former presidents were out in force at Flushing Meadows' Arthur Ashe Stadium to watch could have been Williams final appearance in a Grand Slam singles match.

But the 40-year-old ensured that her legions of fans will have at least one more chance to savor her talents as she dug out victory despite an error-strewn display.

"I feel so comfortable on this court and in front of everyone here," a jubilant Williams said after her victory.

"The crowd was crazy — they really helped pull me through. I was really pumped," added Williams, who won the first of her Grand Slam titles in the same arena in 1999 as a 17-year-old prodigy.

Williams admitted that deciding to walk away from the sport after 27 years as a professional was "such a hard decision."

"I think when you are passionate about something it is always hard to walk away," she said.

"I have been trying to decide what to do. I love this game."

"But I was just like 'Alright, I think now's the time.' I have a family, there's other chapters in life. I call it evolution."

Williams later refused to be definitive about her retirement, however, when asked if the US Open would be her last tournament, teasing the possibility that she may yet play on.

"I've been pretty vague about it, right?" she said.

"I'm going to stay vague because you never know."

A sell-out crowd of 23,500 had roared its appreciation for Williams as she strode into the arena wearing a striking sparkling bodice and black skirt comprised of six layers — one for every US Open title she has won.

The roll-call of A-listers on hand for the occasion included former US President Bill Clinton, Vogue editor Anna Wintour, former heavyweight champion Mike Tyson, tennis legend and Hollywood stars such as Hugh Jackman and Queen Latifah.

Williams acknowledged that leaving the spotlight — whenever that is — would be a wrench.

"The more tournaments I play, I feel like the more I can belong out there," she said.

"That's a tough feeling to have, to leave knowing the more you do it, the more you can shine."

In other women's draw action, former world No. 1 Simona Halep, seeded seventh, was the biggest casualty in the first round, crashing out 6-2, 0-6, 6-4 to Ukrainian qualifier Daria Snigur.

But there were no such problems for US teenager and 12th seed Coco Gauff, who cruised past France's Leolia Jeanjean 6-2, 6-3.

Meanwhile, the men's draw got under way with a stunning upset for Greek fourth seed Stefanos Tsitsipas, who was bundled out by Colombian qualifier Daniel Elahi Galan 6-0, 6-1, 3-6, 7-5.

Earlier, Russia's defending champion Daniil Medvedev routed Stefan Koslov of the United States in the top half of the draw.

The Russian comfortably dispatched world No. 111 Kozlov 6-2, 6-4, 6-0 in two hours and one minute.

Medvedev, bidding to become the first man to defend the US crown since Roger Federer retained the title in 2008, faces France's Arthur Rinderknech in the second round.

Britain's Andy Murray, another veteran well into the twilight of his career, marked the 10th anniversary of his maiden Grand Slam win with a straight sets defeat of Argentinian 24th seed Francisco Cerundolo.

The 35-year-old Scot showed no signs of recent cramping problems in a 7-5, 6-3, 6-3 win, but admitted afterwards: "It felt like five sets."

It was Murray's first straight sets win at a Grand Slam event since 2017.