Philippoussis joined Tsitsipas’ team as a co-coach after Wimbledon last year and has sat in his box in Melbourne this week.
Tsitsipas faces Jiri Lehecka on Tuesday night and is one win away from his fourth Australian Open semi-final berth in five years, but he’s never made the final.
Philippoussis, who made the 2003 Wimbledon final, believes growing “maturity” in Tsitsipas will see him push through this year,
“He’s worked hard, simple as that. The Australian Open comes down to who has been putting in the work in the offseason,” Philippoussis said in an interview with Fox Sports
“We have tablets and stats but I don’t like to look into them too deeply because at the end of the day it’s forehands and backhands.
“If you’re going to tell a guy he likes to go there and does big serves out wide on the ad and he goes down the tee on a break point, he’s going to look at you and be pretty pissed.
“Anything can happen out there, it’s just important to focus and you have to adjust like the great players.
“He’s done well in the past here and he’s got that respect from the crowd, they’re very well educated in their tennis and they love to watch a battle and one thing Stef does is he always leaves it on the court and he’s a great athlete.”
Tsitsipas has been passionately supported in Melbourne and he’ll face unseeded Czech Lehecka at Rod Laver Arena on Tuesday night.