MELBOURNE: Sixth seed Alexander Zverev mangled a racquet in frustration as he was made to dig deep against Marcos Giron before reaching the Australian Open second round Monday.

The German, a semi-finalist last year who is gunning for a maiden Grand Slam title, lost a tight first set against the 73rd-ranked American before grinding to a 6-7 (8/10), 7-6 (7/5), 6-3, 6-2 win.

It was a tougher assignment than expected with Zverev smashing his racquet in anger during the second set before regaining his composure.

"He played incredible. He had me on the ropes, particularly in the second set tie-break," said Zverev, who is into round two for a fifth straight year.

"I was just happy to get through. Playing the first round of a Grand Slam is never easy. My body felt a little fatigued, I was a little tired."

He will meet either Japan's Taro Daniel or American qualifier Maxime Gressy next.

The 23-year-old came into the tournament having beaten world number 12 Denis Shapovalov in the ATP Cup last week while pushing top-ranked Novak Djokovic deep into a third set, before being beaten by fourth-ranked Daniil Medvedev.

He is looking to become the youngest Grand Slam singles champion since Djokovic won the title at Melbourne Park in 2011.