Tennis great Patrick Rafter has backed teenage sensation Nick Kyrgios to make a charge to the world's top 10 "purely on talent", saying he's been tough on the Canberra star to help him stay composed on the court.
Kyrgios will get his chance to shine on centre court at the US Open when he takes on world No. 18 Tommy Robredo on Sunday morning.
The 19-year-old will become Australia's top-ranked player after the tournament, soaring into the top 50 and jumping ahead veteran Lleyton Hewitt.
But Australian Davis Cup captain Rafter says a raw Kyrgios has only scratched the surface on his potential, insisting he is still learning and won't hit peak form for another two years.
Kyrgios was one warning away from disqualification in his round-one win over Mikhail Youzhny, but then turned his on-court frustrations into a scintillating display to beat Andreas Seppi on Friday.
"I think Nick now realises how he can play and keep composed," Rafter said. "Nick has to learn and he's done well to listen over the past three or four months. I've been pretty tough on him because I don't want him to be known as someone who is volatile.
"He's young and dealing with high-pressure situations, it's more about learning things as we go along. I'll pull him aside if I think he oversteps the mark a bit.
"I think he's got as good a chance against Robredo as he did in the first two matches. He'll be fine."
Kyrgios has rocketed out of obscurity to become the pin-up boy for Australian tennis.
Less than two years ago he was ranked outside the world's top 800 players, but the former junior world No. 1 will reach a career high mark after the US Open.
Kyrgios thrives on the big stage and he'll get his chance to impress again when he takes on Robredo, the man who beat Roger Federer at the US Open last year.
If he beats Robredo he will set up a round-of-16 clash against Australian Open champion Stan Wawrinka.
Kyrgios' outstanding performance at Wimbledon last month, which included beating Rafael Nadal, proves he can match with the world's best players.
He has smashed 48 aces in seven sets in New York, but two-time US Open winner Rafter believes Kyrgios can get even better.
"Nick seems to be someone who doesn't need to play a lot and can then be successful," Rafter said.
"I think we're a couple of years until he's up there with fitness and strength, that will come in time when his body allows him to work harder and tougher mentally.
"Nick will be playing his best tennis in a couple of years. If by the end of the year he's top 10, if we say something crazy like that, then he's done it purely on talent.
"He's got a lot more to work on, he's still pretty raw and there are areas he can fix up."
Rafter believes Kyrgios' fast rise has pushed Bernard Tomic to be better.
A hip injury forced Tomic to prematurely end his US Open campaign on Saturday, and it could have an impact on Rafter's Davis Cup plans for the tie against Uzbekistan in Perth from September 12.
Rafter and Kyrgios have teamed up as Bonds ambassadors. But Rafter says he will limit his input to Kyrgios' game to ensure he doesn't cloud the young star's mind.
"I've probably done enough talking, he's heard from me and he knows how I feel on certain issues," Rafter said.
"The rest is up to him. I don't think I'll have to talk to him in that role any more, it's more in the development of his game and, if he's ever got questions or queries, then I'll help out.
"I'm there for him if ever he needs me. He's growing up and maturing, that will come naturally in time. It's the whole package – physically and mentally – and that's a couple of years away."
