MELBOURNE — Alexander Zverev believes Dominic Thiem is playing well enough to trouble seven-time champion Novak Djokovic in the Australian Open final after his victory over four tough sets on Friday.

Zverev, the seventh seed, took the first set against fifth-ranked Thiem but the Austrian's supreme fitness and greater experience helped him win 3-6, 6-4, 7-6 (7/3), 7-6 (7/4).

Zverev, 22, who was gunning to became the youngest man in a Grand Slam final since Andy Murray in Melbourne in 2010, said two-time French Open finalist Thiem was playing some of his best tennis.

"I think he has a chance in the finals, if he's physically fine. He did play a lot of long matches. But, yeah, we'll see," he said.

"He's playing the best tennis of his life. I think he's playing much better than he played in London (at the ATP Finals), to be honest."

Thiem beat Zverev in the last four at the season-ending ATP Finals, only to lose to Stefanos Tsitsipas in the title match.

Thiem knocked out Rafael Nadal in the quarterfinals but he will need to lift again to beat Djokovic in the final on Sunday, with the Serb on a 12-match unbeaten streak this season.

Zverev admitted he didn't play his best at crunch moments Friday and it cost him dearly as he exited the Australian Open after his best ever performance at a Grand Slam.

He noted that he had 14 break point chances and only converted five of them.

"I had a lot of chances. I had 14 break points. That should be plenty. In the important moments, I didn't play my best. He did," he said.

"That's where the match kind of went his way. We've had a lot of tight moments, four tight sets. In the third set I had set points. In the fourth set, I had chances. I've just got to execute better next time."

Despite his disappointment, it was the furthest he had got in 19 Grand Slams, with a more relaxed approach helping him achieve the feat, something he said would bode well in the future.

"I mean, it was a great tournament, great match today," he said.

"I came to this tournament different after not playing my best. I went step by step, match by match. Usually I didn't do that in Grand Slams.

"Maybe I can take that away, but right now I'm still a little bit disappointed about the match."

Zverev had pledged $10,000 for each of his wins to the victims of Australia's bushfires, as well as all A$4.12 million ($2.83 million) if he won the final on Sunday.

"Unfortunately I could not make it happen with all the prize money," he said. "As I said, I will keep my promise. I will donate the $50,000 and hope that can help a little bit." — AFP