Thanasi Kokkinakis has dug deep at the US Open to post his first main-draw win at a grand slam event in more than four years.

The injury-plagued Australian overcame the disappointment of failing to serve out the first-round match in the third set to tough out a 6-3 7-6 (10-8) 6-7 (4-7) 6-2 victory over Ilya Ivashka on Tuesday.

The 24-year-old Kokkinakis slugged it out with the Belarusian qualifier for almost four hours to earn a second-round shot at Rafael Nadal.

The emotional triumph, after a diabolical run with injuries, was his first main-draw win at a slam since an epic five-set comeback victory over compatriot Bernard Tomic at the 2015 French Open.

It was also Kokkinakis’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.

Kokkinakis appeared to be heading for a straight-sets victory after winning a pulsating second-set tiebreaker with a broken string.

Desperate to finish the point quickly after snapping the string, Kokkinakis scrambled to the net and somehow won the rally with a forehand overhead, provoking rousing applause from the Court 6 crowd.

The world No.203 served for the match at 6-5 in the third set but couldn’t buy a first serve when it mattered, then lost the breaker.

But he rebounded to break the Belarusian twice in the fourth set to prevail after three hours and 48 minutes of quality tennis.

Alexei Popyrin serves against Argentina’s Federico Delbonis. Photo: Getty

Meanwhile, Alexei Popyrin is staying cool as opportunity knocks for Australian tennis’s hottest young prospect in New York.

Popyrin, who only turned 20 this month, surged into the second round of the US Open for the first time with an impressive straight-sets victory over the vastly more experienced Federico Delbonis.

Popyrin notched yet another milestone in a breakout season with his 6-1 7-5 7-6 (7-5) triumph over the Argentine on Tuesday.

After cracking the world’s top 100 for the first time, then earning direct entry into a major for the first time, Popyrin has now reached at least the second round at all four grand slams in 2019.

“It’s a great achievement for me,” said the former French Open junior champion.

“It’s just the vibe of grand slams. I really enjoy playing grand slams – the big crowds, the big courts, the big stadiums, even though I didn’t play on one today.

“I had a good crowd out there today. Some of the Aussie support, I still heard it, even if it was on a small court.”

Should he cash in on his good fortune, Popyrin could square off with countryman Jordan Thompson for a spot in the second week.

Thompson’s 6-3 6-2 6-4 victory over Joao Sousa booked Popyrin’s fellow Sydneysider a second-round date with Italy’s 24th seed Matteo Berrettini.

“That’s probably one of the best matches I’ve ever played – from the get-go,” Thompson said.

“Served pretty well, made a lot of returns – (on) first and second serves – and executed the game plan, so really happy to get through that one.”

In a mark of how far Thompson has come, the 25-year-old – who cracked the world’s top 50 last month for the first time – needed five sets to see off the 44th-ranked Sousa last time they met.

Beaten but not broken, John Millman said he wouldn’t trade being pummelled by Rafael Nadal on one of tennis’s grandest stages for anything in the world.

“I’ve still got a story. Definitely a good story,” Millman said after succumbing 6-3 6-2 6-2 to the 18-times major winner in the US Open first round.

And that he does.

Millman can tell his grandkids one day that he was the first – and possibly only – player to face all-time greats Nadal, Roger Federer and Novak Djokovic in consecutive matches at the same major tournament, albeit over two years.

The affable Australian famously took down Federer in the fourth round last year before making Djokovic fight for his quarter-final victory en route to the title.

“How lucky am I with my career? I’ve played all the big guys on the biggest courts in the world,” said Millman, who has also jousted with Andy Murray on Wimbledon’s hallowed centre court.

On the women’s side of the draw, Ajla Tomljanovic was left pinching herself after mounting a miraculous fightback to join Ashleigh Barty in the second round of the US Open.

Ajla Tomljanovic of Australia reacts against Marie Bouzkova of the Czech Republic. Photo: Getty

Tomljanovic looked headed for the exit gates when she trailed Czech Marie Bouzkova 6-1 5-2 only to stage a great escape that not even she could believe.

From the brink, the Australian No.2 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.”

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.

-AAP