MELBOURNE: Sixth seed Alexander Zverev survived an almighty scare at the Australian Open on Thursday as the former semi-finalist dug deep to beat Slovakian qualifier Lukas Klein 7-5 3-6 4-6 7-6(5) 7-6(7) and move into the third round.

Rain forced the contest to be completed under the roof on John Cain Arena and Zverev found himself in big trouble as world number 163 Klein turned up the pressure after losing the opening set to take the next two.

The 25-year-old Slovak, whose only previous Grand Slam main draw appearance was at Wimbledon in 2022, inched towards his first career top-10 win but squandered the chance to break at 4-4 in the fourth set.

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Zverev levelled the contest as Klein frittered away a 3-1 lead in the tie-break and the 26-year-old German swapped breaks with his opponent early in the decider before holding his nerve in a tie-break to prevail.