New York, United States, 28 August 2019 | Darren Walton (AAP)

Thanasi Kokkinakis dug deep on Tuesday to post his first win in a Grand Slam tournament main draw in more than four years.

The injury-plagued Australian wildcard overcame the disappointment of dropping the third set after serving for the match to tough out a 6-3 7-6(8) 6-7(4) 6-2 first-round US Open victory over Ilya Ivashka.

The 24-year-old slugged it out with the Belarusian qualifier for almost four hours to earn a second-round shot at Rafael Nadal, who beat fellow Australian John Millman in straight sets at Arthur Ashe Stadium.

Earlier on Tuesday, Australian No.2 Ajla Tomljanovic pulled off a miracle comeback to join Ash Barty in the second round.

In what has been a fruitful Day 2 for Australia, Tomljanovic and Kokkinakis joined Jordan Thompson and Alexei Popyrin as first-round winners, making it six Aussies through to the second round of the men’s and women’s singles draws.

For Kokkinakis it was an emotional triumph after a diabolical run with injuries, marking his first success at a major since an epic five-set comeback win over Bernard Tomic at the 2015 French Open.

“It was a hell of a feeling,” Kokkinakis said. “Obviously I feel like I’ve had a lot of my tennis career so far, to this point, taken away.

4 damn years #persistentmfer @usopen pic.twitter.com/Knx4RxXEAd

— Thanasi Kokkinakis (@TKokkinakis) August 28, 2019

“I knew the first two sets, getting those under my belt was going to be big. Luckily I got the second set after I broke a string on set point.

“What are the odds? I’ve probably been playing for two hours and then on that point it breaks but, you know, that’s tennis. It’s definitely a massive relief.”

It was also the world No.203’s first victory at Flushing Meadows, having lost a sapping five-setter to Janko Tipsarevic two years ago and being forced to retire with cramps in the deciding set against Richard Gasquet in 2015.

His reward is a big one: a show-court blockbuster with three-time champion Nadal on Thursday after the Spaniard beat Millman 6-3 6-2 6-2 in his opener.

“I give myself a chance for sure. It’s going to be tough – very physical but I’m ready for it,” Kokkinakis said.

“I know what he brings. I’ve seen him play enough, I hope. I’m going to play my game and see what happens.”

Tomljanovic back from the brink

Tomljanovic was left pinching herself after mounting a miraculous fightback; she trailed Czech Marie Bouzkova 6-1 5-2 only to stage a great escape that not even she could believe.

From the brink, Tomljanovic reeled off eight straight games to assume control before prevailing 1-6 7-5 6-1.

“At 6-1 5-2, I just kind of thought ‘OK, this isn’t the best day’. I didn’t even think about winning,” Tomljanovic said.

“I just thought maybe I can get one point, and then a second point, and just take it one point at a time. I actually thought that made my game better. I maybe changed my game style a little bit and I saw success with that. I’m really happy that I got through.

“I’ll be honest. I didn’t think I would at some point make it.”

Bouzkova came into the match in great form, having reached the semifinals of the WTA event in Toronto and stretching Serena Williams to three sets before bowing out.

Linette too strong for Sharma

While world No.47 Tomljanovic can look forward to showdown on Thursday with Estonian Anett Kontaveit, the 21st seed, after winning her opener at Flushing Meadows for the third-straight year, West Australian Astra Sharma bowed out.

Riding an eight-match winning streak after collecting her maiden WTA title as a qualifier last week at The Bronx, in-form Pole Magda Linette was too hot for Sharma, winning 6-3 6-4.

“Magda played a really good match. She’s obviously come off some really good matches. She played cleaner and better than me today,” Sharma said.

“But getting to play the main draw of all the slams (this year) has been amazing, they’ve all been good learning experiences.

“It gives me an idea of what I need to do to get back to this level and maintain it and get better.”