Kei Nishikori advances to 3rd round at Australian Open

Melbourne: Japan's Kei Nishikori says he's closing in on his best form after being pushed to four sets to put away Croatia's Ivan Dodig and reach the third round at the Australian Open on Thursday.

Fifth seed Nishikori, who is knocking on the door for a Grand Slam title after losing to Marin Cilic in the final of last year's US Open, won 4-6, 7-5, 6-2, 7-6 (7/0) and will now play American Steve Johnson.

"I think I'm getting close. Maybe these couple of matches I didn't play 100 percent, but I'm still winning good three and four sets. I think it's getting there," Nishikori said after his latest win.

"I'm playing good. For sure this match will help for my next match. Trying to be 100 percent little by little."

Nishikori had a solid 2hr 47min workout on the hottest day of the tournament so far, but said he was looking forward to stepping up his campaign in his next outing against Johnson.

"It was different than the first day. It was much warmer.

"Hot out there. It wasn't easy," he said.

"Especially in the third and fourth sets, I was a little bit dizzy and tired. But it's going to be like this in Australia, so I think I was ready for it.

"Hopefully, I won't play in these conditions again. Try to get healthy tomorrow."

Nishikori beat Johnson over two sets in the lead-up Brisbane International event this month and said he would be ready for the American.

"He's a tough player. Good serve. Really good serve.

"Coming to the net a lot and big forehand, so I have to be careful about a couple things to play against him," he said.

Nishikori said he felt like he was playing at home with a Japanese-dominated crowd cheering his winners inside Hisense Arena in the sauna-like conditions.

The Japanese star broke the 86th-ranked Dodig five times, the last time when the Croat was serving to take the match into a fifth set.

Nishikori forced a fourth-set tiebreaker and romped through it without dropping a point to clinch victory, hitting 52 winners and making only 26 unforced errors over the four sets.

"It was very warm conditions today and he was playing really well, very aggressive, good returns and it was a tough battle," Nishikori said.

"It was very close and it could have gone five sets.

"It's been a good two matches here and I'm feeling really well so hopefully I can win here over the next two weeks. I felt like I was in Japan such was the crowd's support today and I was very happy to be playing on this court."