Nick Kyrgios has cast friendship aside by defeating doubles partner Thanasi Kokkinakis for a spot in the second round on an emotional day at the US Open.

Kyrgios clinched the win in a tiebreaker to take a 6-3 6-4 7-6 (7-4) at Arthur Ashe Stadium on Tuesday Australian time, just a couple of hours after wild scenes greeted Serena Williams as she defied predictions win her opening march.

Kyrgios broke Kokkinakis in each of the first two sets, then clinched the win in a tiebreaker to take bragging rights in the all-Australian affair.

Afterwards, he said the match was a “nightmare”, despite his easy win.

“I played a really good first couple of sets, got on top of the match early,” Kyrgios said.

“When we saw the draw, it was a nightmare, honestly. We never want to play each other and he probably beats 80 per cent of the draw tonight, he’s been playing really good.

“I’ve just got so much respect for him so I can’t wait to get out there and play doubles with him on the right side of the net in a couple of days.”

The fuss-free victory, after Williams’ drama-charged triumph in the preceding match, completed a fine opening day for Australia, with Alex de Minaur, Ajla Tomljanovic and Jordan Thompson also advancing.

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Kokkinakis, John Millman – in five gruelling sets in scorching heat – and Daria Saville were the only casualties.

Kyrgios, though, was the most impressive of the four winners.

The Wimbledon finalist was untouchable on serve, not offering a single break point all match and barely giving Kokkinakis a look in on his deadly delivery.

As well as clearing one big hurdle with success over his great mate, Kyrgios also had two other danger men removed from his section of the draw.

Kyrgios will next meet Frenchman Benjamin Bonzi, followed by a seed-free path to a possible last-16 showdown with world No.1 and defending champion Daniil Medvedev.

Williams not ready to go

In her first match at what is expected to be the last US Open – and last tournament – of her remarkable playing career, Williams overcame a shaky start to overwhelm Danka Kovinic 6-3 6-3 in an atmosphere more akin to a festival than a farewell.

Looking ahead to a future without tennis competition, Williams told the crowd: “There’s other chapters in life.”

Williams was not at her best early on against the 27-year-old world No.80 from Montengero. Maybe it was the significance of the moment. There were double-faults, other missed strokes, missed opportunities.

Trailing 3-2 in the first set, Williams, who turns 41 in less than a month, suddenly looked a lot more like someone with six championships at Flushing Meadows and 23 grand slam titles overall as she staged her comeback.

She rolled through the end of that opening set, capping it with a service winner she reacted to with clenched fists and her trademark cry of “Come on!”

The more than 23,000 in the stands (thousands of others watched on a video screen outside) rose for a raucous standing ovation – and did so again when the one-hour 40-minute contest was over, celebrating as if another trophy had been earned.

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Instead, there is plenty more work to be done. Williams will play in the second round against No.2 seed Anett Kontveit on Thursday after the Estonian beat Jaqueline Adina Cristian of Romania 6-3 6-0.

And there’s also doubles to come, too. Williams and her sister, Venus, are entered together in that competition, with their initial match slated for Wednesday or Thursday.

“Just keep supporting me,” Williams said, “as long as I’m here.”

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After Kovinic was introduced simply by name, making clear to even her what an afterthought she was on this muggy evening, Williams’s entrance was preceded by a tribute video narrated by performer Queen Latifah, who called the American the “Queen of Queens.”

The arena announcer called Williams “the greatest of all time,” and intoned: “This US Open marks the final chapter of her storied tennis history.”

Her daughter, Olympia, who turns five on Thursday, wore white beads in her hair while sitting with her father and grandmother in the stands, a nod to her mother’s hairstyle when she won her first US Open in 1999 at age 17.

“It is so difficult to really capture what Serena and Venus have done for the sport of tennis,” Stacey Allaster, the tournament director of the American grand slam event, said.

“They have transformed our sport. They’ve made us more inclusive. And they’ve transcended sports.”

-with AAP