Kei Nishikori has allayed any lingering fitness concerns with a fighting five-set first-round win at the Australian Open.

The Japanese fifth seed battled hard to deny Russian Andrey Kuznetsov 5-7 6-1 6-4 6-7 (6-8) 6-2 on Monday to reach the second round.

Nishikori hadn’t played since losing the Brisbane International final nine days ago after withdrawing from an exhibition event in Sydney last week with a hip injury.

The Asian superstar’s three-hour, 34-minute marathon was in stark contrast to his next opponent’s walk in the park.

Frenchman Jeremy Chardy only spent four games on court before Nicolas Almagro retired hurt trailing 4-0 in the first set of their first-round match.

But Nishikori said he hoped to back up fine on Wednesday when he takes on Chardy for a place in the third round.

“I was feeling okay. Feeling really good after I got hurt in Brisbane and I think I was ready for play today,” Nishikori said.

“(It was) unfortunate to play five sets in long match, but, yeah, should be okay for next one.”