Australian Open 2021: Thiem overcomes Kukushkin hurdle; Zverev grinds down Giron

US Open champion Dominic Thiem was given an unexpectedly tough test as he kicked off his bid for a maiden Australian Open title Monday, pressed hard by Kazakh veteran Mikhail Kukushkin before racing to the finish line.

The third-seeded Austrian, a narrow loser to Novak Djokovic in last year's Melbourne final, came through his match on Rod Laver Arena 7-6 (7/2), 6-2, 6-3, but was made to work for it.

"It's interesting because it's the first time I've met him and there's not too many I didn't meet on tour," said Thiem of his opponent.

"He's very experienced and the first set was super-challenging. But, in general, I'm very happy to be back and have success in the first round."

Kukushkin, 33, had lost his opening-round match at Melbourne on 11 of his previous 12 appearances.

Thiem will next play either German Dominik Keopfer or Bolivia's Hugo Dellien, with Australia's Nick Kyrgios looming as a potential third-round opponent.

Now 27, the baseliner finally cracked the big time when he produced a historic comeback to beat Alexander Zverev in the US Open final last year.

He is in Melbourne without his coach Nicolas Massu, who tested positive for the , and is instead working under his father, Wolfgang.

Meanwhile, 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.