Kei Nishikori survived a dramatic Australian Open first-round match Tuesday after his Polish qualifier opponent retired with cramp in the searing Melbourne heat having raced to a shock two-set lead.

Eighth seed Nishikori of Japan won 3-6, 6-7 (6/8), 6-0, 6-2, 3-0 but the scoreline fails to tell the story of world number 176 Kamil Majchrzak's torrid end to the match.

Majchrzak had never before played in a Tour-level event other than Davis Cup ties but showed no sign of nerves against Nishikori, who won his 12th ATP Tour at the Brisbane International warm-up.

It was the young Pole's first ever match against a top 50 opponent but you would never have known it as he took a two-set lead with a succession of blistering winners off both wings.

"I have to say he had it today," conceded Nishikori. "He played very well and it was unfortunate how it finished.

"I didn't do anything, but he was hurt and I feel sorry for him."

At the start of the third set with temperature pushing into the mid 30s Celsius, the 23-year-old began to cramp so badly that he could hardly grip his racquet.

The physio was called and gave Majchrzak some pickle juice to drink after he reported pain in both thighs, both arms and his right hand.

It was a heart-wrenching sight as a tearful Majchrzak was left almost unable to move and the former US Open finalist Nishikori dropped only six points as he professionally eased to the third set 6-0.

Majchrzak had more treatment and was given some medication and massage which helped him emerge for the fourth.

He finally began to regain some movement and broke a run of 10 consecutive losing games to a huge cheer.

But Majchrzak had nothing more in the tank and sensibly called it a day midway through the fifth set leaving Nishikori to thank his lucky stars he made it through.

"I was trying to play but he was playing amazing tennis (in the first two sets)," said Nishikori, who has previously made three Grand Slam semi-finals.

"I have to be happy that I didn't lose today," added the Japanese, who missed the Australian Open last year due to a wrist injury. 

On his last appearance in 2017, he reached the last-16, falling to Roger Federer in five sets. 

The Japan number one will now play Croatian world number 71 Ivo Karlovic or another Pole, Hubert Hurkacz, in the second round.

Results from Day 2 of the Australian Open on Tuesday:
                  
Men's singles
1st round
Ryan Harrison (USA) bt Jiri Vesely (CZE) 6-0, 7-5, 6-3
Daniil Medvedev (RUS x15) bt Lloyd Harris (RSA) 6-1, 6-2, 6-1
Fabio Fognini (ITA x12) bt Jaume Munar (ESP) 7-6 (7/3), 7-6 (9/7), 3-1 retired
Leonardo Mayer (ARG) bt Nicolas Jarry (CHI) 7-6 (7/4), 7-6 (7/3), 4-6, 6-3
Ilya Ivashka (BLR) bt Malek Jaziri (TUN) 4-6, 7-6 (8/6), 6-1, 4-0 retired
Ivo Karlovic (CRO) bt Hubert Hurkacz (POL) 6-7 (5/7), 7-6 (7/5), 7-6 (7/3), 7-6 (7/5)
Kei Nishikori (JPN x8) bt Kamil Majchrzak (POL) 3-6, 6-7 (6/8), 6-0, 6-2, 3-0 retired
Alexander Zverev (GER x4) bt Aljaz Bedene (SLO) 6-4, 6-1, 6-4
Alex Bolt (AUS) bt Jack Sock (USA) 4-6, 6-3, 6-2, 6-2
Gilles Simon (FRA x29) bt Bjorn Fratangelo (USA) 7-6 (7/2), 6-4, 6-2
Pierre-Hugues Herbert (FRA) bt Sam Querrey (USA) 5-7, 7-6 (8/6), 6-3, 6-1
Borna Coric (CRO x11) bt Steve Darcis (BEL) 6-1, 6-4, 6-4
Marton Fucsovics (HUN) bt Albert Ramos (ESP) 6-3, 6-4, 6-7 (5/7), 6-3