Bernard Tomic believes he can continue his career-best run after crashing through the physical and psychological pain barrier to end Lleyton Hewitt's glittering US Open career.

Tomic saved two match points in an epic all-Australian second-round encounter to reach the third round for the first time at Flushing Meadows with a sapping 6-3, 6-2, 3-6, 5-7, 7-5 win on Friday.

The 24th seed had to pull out all the stops to deny his Davis Cup teammate and mentor an extraordinary 33rd five-set triumph on another punishing day at the Open.

Hewitt, who will retire after the Australian Open in January, overcame a hip injury to rally back from two sets and a service break down to serve for the match at 5-4 in the fifth.

But Tomic, 12 years his junior and ranked 331 places above the former world No 1, dug deep to reel off four games straight to take the match after three hours and 27 minutes.

"It was not going to be easy because I kept thinking about watching his matches in the past, how he got out of them," Tomic said. "Then I was in the moment, in the position where I was winning and he was starting to get back.

"It is so difficult playing him. I was very, very nervous [and] it could have gone both ways.

"He is a huge legend to me. I always looked up to him. It was very emotional."

And painful, with Tomic calling the trainer to rub his aching legs at 6-5 in the deciding set then consoling - and congratulating - his hero at the net.

"In my mind, I thought he won the match," Tomic said. "It was very emotional for us. He wished me the best of luck. I'm very good friends with him. For me, it's not easy to see that."

Hewitt said he hoped his grit and the manner of Tomic's fighting win would help the Australian No 1 - who is projected to climb to a career-high No 22 after the Open - grow as a player.

"He obviously was well on top and I was able to somehow find a way. That's what I've been renowned for in my career," Hewitt said.

"If I can instil a little bit of that especially into the three promising young guys on the way up, with their games and the weapons they have, then that's just another positive."

Next up is Richard Gasquet, a four-set winner over Dutchman Robin Haase, and Tomic believes he has the arsenal and energy to take out the French 12th seed and make the second week.

"I spoke to him in the locker room," Tomic said.

"He was, as well, very tired. He was feeling some problems out there. Everyone is feeling problems. I think my record is 4-1. I beat him in a very important one, which is Wimbledon, third round, 2013.

"Every match we had in the past was very close. I've learned a lot when I played him. He's an amazing player. He's not easy to play.

"I have to take each match that I played against him and use it for this third-round match." - AAP