Carlos Alcaraz rued missed opportunities after coming up short against Alexander Zverev in a thrilling Australian Open quarter-final early Thursday but said he could leave Melbourne with his head held high.

The world number two threatened a stunning comeback on Rod Laver Arena after being outplayed for nearly three sets by the German but in the end went down 6-1, 6-3, 6-7 (2/7), 6-4.

Alcaraz had stormed into the last eight for the loss of just one set but struggled against the laser-like Zverev serve and could not get a foothold in the match.

But, seemingly down and out, he broke the sixth seed as he served for the match at 5-3 in the third set and produced breathtaking tennis in the tie-break.

Despite huge support from a rapt crowd, he was unable to maintain his stellar level and two breaks in the fourth set took Zverev over the line.

Alcaraz said he played "great tennis" at the end of the third set but his level had dipped.

"I played good tennis in the fourth set," he said. "Obviously not to my best level but, you know, it was a good one.

"Didn't make my chances. You know, a lot of ups and downs with my level, with my tennis, with the serves."

It is an early exit by the standards of the 20-year-old. He missed last year's Australian Open with an injury but reached the semi-finals of the French Open before winning Wimbledon and then making the last four at the US Open.

But Alcaraz said overall he was pleased with his work in Melbourne.

"In general, you know, I leave the tournament happy, forgetting about today's level," he said. "But in general I think I did a pretty good tournament.

"I played great matches and obviously a quarter-final of a Grand Slam is good. It is not what I'm looking for, but is not bad, you know."

Energy 

Alcaraz said the energy of the fans had lifted him when it looked as though he was sinking to a straight-sets defeat.

"I think there was a fourth set because of the crowd, and the way that they bring energy to me," he said. "It was crazy.

"I was down, totally down, and they started -- or they didn't stop supporting me, so it was crazy.

"So I want to thank them, you know, to stay there, believing in me, supporting me in every ball, in every point."

Alcaraz was the only man to beat world number one Novak Djokovic at Grand Slams last year -- in the Wimbledon final -- but he said the players remaining in the draw have the ability to beat the Serbian 10-time Australian Open champion.

"It's not easy to beat Novak in a tournament, but I think it's even tougher in a Grand Slam," he said. "But he has to face (fourth seed) Jannik Sinner -- he's playing an unbelievable game.

"He has not dropped a set in this tournament. That means that he has the level and the capacity to beat Novak."

Zverev will face third seed Daniil Medvedev in the other semi-final on Friday.