Kei Nishikori lamented being pushed to five sets by Andrey Kuznetsov in a first-round scare at the Australian Open.

The Japanese fifth seed was challenged before edging past Kuznetsov 5-7 6-1 6-4 6-7 (6-8) 6-2 in hot conditions at Melbourne Park on Monday.

Nishikori needed three hours, 34 minutes to advance and the 2014 US Open runner-up believes he should have completed the job more easily.

"I think I let him come back in the fourth set. I should have finished that set," he said.

"I was up in the tie-break, but I think he played well from the beginning.

"Fifth set I started playing much better. It was tough, a really tough match."

Awaiting Nishikori in the second round is Jeremy Chardy, the Frenchman who was on court for just 23 minutes and led Nicolas Almagro 4-0 before the Spaniard retired.