Defending champion Stan Wawrinka frittered five match points before sealing a straight sets win over Japanese superstar Kei Nishikori to reach the semi-finals at the Australian Open on Wednesday.

The Swiss fourth seed won 6-3, 6-4, 7-6 (8/6) in just over two hours and will now face either world number one Novak Djokovic or eighth seed Milos Raonic for a place in Sunday's final.

Nishikori had mastered the Swiss over five sets in the quarter-finals at last year's US Open, but it was a far different outcome this time.

Wawrinka dominated with his serve and backhand to reach his third Grand Slam semi-final and a chance of playing in back-to-back finals at the Australian Open.

He broke Nishikori's service three times and lost serve only once, while winning 86 percent of his first-serve points.

Wawrinka looked set to romp away with the tiebreaker in the final set, holding five match points at 6-1 only to tighten up and almost throw it away.

"When he came back from 6-1 to 6-6 he was playing good, aggressive. I was a little bit hesitant," Wawrinka said

"I didn't put in first serve. It's never easy when you have so many match points to focus after.

"But at 6-6 I had the wind again. I was trying to be aggressive. I was lucky that he missed the dropshot and happy to make an ace after."

Wawrinka would have slipped from four to 10th in the rankings if he had lost and still has a huge task ahead to defend his title.

"I'm more aggressive. I'm more confident with my game when I come to the net," he said. "It's a Grand Slam. You play every two days. Today was a great level, was a great match.

"I'm going to enjoy it a little bit, watch who's going to win tonight and get ready for the semi-final."

Early breaks

Wawrinka set out to attack Nishikori's forehand and got a service break in the fourth game after the 25-year-old netted a forehand.

The Japanese star fought off two set points in the eighth game before Wawrinka served out for the opening set.

Nishikori again came under pressure in the second set, fighting off a break point in the third game before he was broken in the fifth by a scorching Wawrinka backhand winner.

The Japanese star saved three break points in his next service game before Wawrinka served out for a two sets to love lead.

The US Open finalist jumped out to a 2-0 lead in the third set, but the Swiss quickly broke to love with a cracking backhand cross-court winner and then levelled up.

Both players swapped breaks early in the third set before Wawrinka stormed to five match points in the tiebreaker.

But he lost them all before Nishikori attempted a netted drop shot from the baseline to set up another match point.

Wawrinka made no mistake with an ace to clinch victory.

"I know I now have a Grand Slam trophy at home. I also won the Davis Cup. I have confidence from that," said the Swiss.

"I know I can make it. I trust my game. I trust myself on the court even when we start to play in a semi-final or final at a Grand Slam."