MELBOURNE, Jan. 21 (Xinhua) -- Third seed Alexander Zverev reached the Australian Open third round in unconvincing fashion after a battling four-set victory over France's Alexandre Muller on Wednesday.

In the night session on Rod Laver Arena, the German finally prevailed 6-3, 4-6, 6-3, 6-4 in just over three hours.

It continued a tough start to the tournament for Zverev, last year's beaten finalist, after he was similarly pushed to four sets by Gabriel Diallo in the first round.

Zverev did have an injury scare after requiring medical attention in the fourth set for a leg injury and he needed a painkiller to get through the match.

"I'm extremely happy with this match. This is my favorite court," Zverev said.

After the 52nd-ranked Muller levelled at one-set apiece, the match was halted in the third set due to rain cascading onto the court.

The break seemingly helped Zverev, who lifted his level under the closed roof after the resumption and he sealed the match with an ace.

Zverev will next face 26th seed Cameron Norrie. ■