Melbourne, Australia (SportsNetwork.com) - Stan Wawrinka kept his hopes of a repeat Australian Open title alive by besting fifth-seeded Kei Nishikori in straight sets on Wednesday.

The fourth-seeded Wawrinka fired 20 aces and was broken just once in the 6-3, 6-4, 7-6 (8-6) quarterfinal victory at Rod Laver Arena.

A five-set thriller was played between Wawrinka and Nishikori at last year's U.S. Open, and it was Nishikori who survived the 4-hour, 15-minute marathon.

The evenly-matched opponents were on the court for less than half that in this one.

The defending champ dominated the first set and did not face a break point until he was serving out the second ahead 5-4. Nishikori had three chances at pulling even, but Wawrinka's overpowering serve closed it out.

Nishikori finally earned a break early in the third, but Wawrinka countered with one of his own at love. Three aces early in the tiebreak helped Wawrinka jump out to a healthy 6-1 lead.

After staving off five match points, Nishikori hit a drop shot that fell into the net, and Wawrinka finished him off with another big ace.

Wednesday's nightcap at Rod Laver Arena features top-seeded Novak Djokovic and eighth-seeded Milos Raonic.

Djokovic, who is 4-0 versus Raonic, is seeking an eighth Grand Slam title. He captured three straight Aussie crowns from 2011-13.