The Spurs captain looks revitalized as his side aims for a fourth consecutive league win against Manchester City on Wednesday.
Postecoglou sees no signs of decline in the 32-year-old, whose two assists for Brennan Johnson against Ipswich have put him on track for his best-ever creative season.
On his skipper, Postecoglou said: “No idea but Sonny’s benefitted from the fact he’s been able to have a break between games.
“We saw that on the weekend, after being able to recover from one game to another and having a full week to get his energy levels back, he was outstanding, particularly in the first half.
“And he was great before. You never want to try to predict with players like Sonny how long he will go for because those kind of players I think always defy whatever odds there are because of the way they look after themselves and conduct themselves, the levels.
“Even this year, as difficult as it has been for us, I think his numbers still stack up. You weigh him up against any winger in the league, he’s still going to be top five. He’s probably been top five in the nine or ten years he’s been here.
“Not many would rank with Sonny in terms of output on a consistent basis from his position. He’s top 10 percent of players in his position in the Premier League. Those are the facts and if he’s continuing to do that, there’s nothing to say he should slow down.”