Nishikori out as Keys, 19, makes Australian Open semifinals

Asia's No. 1 Kei Nishikori became another casualty of Stan Wawrinka's Australia Open title defence on Wednesday after the Japanese fifth seed was beaten for speed and execution.

Nishikori could not replicate the thrilling five-set victory he had against the world No. 4 at last year's US Open and instead exited with a 6-3, 6-4, 7-6 (8-6) quarterfinal loss.

In the women's quarterfinals, teenager Madison Keys overcame injury and nerves to upstage one of her idols, Venus Williams, and advance to her first Australian Open semifinal.

To progress further, Keys will have to beat another idol, Venus' sister Serena, who was devastating in her 6-2, 6-2 destruction of 2014 finalist Dominika Cibulkova.

Nishikori often looked rushed until changing to a more aggressive style in the third set.

Asia's first Grand Slam finalist broke early in the third - only to give up his serve immediately after.

He held his ground throughout the remainder of the third and was able to rein in a lightning start by Wawrinka in the tiebreaker.

But after playing Wawrinka out of the point at 6-all, Nishikori netted a horrible drop shot to hand him a sixth match point.

Rather than feel overwhelming disappointment, last year's US Open finalist said he had gained a lot of experience during his equal best result at Melbourne Park.

"It wasn't really a bad week," said the world No. 5. "It's not easy to come to a Grand Slam quarterfinal. I have to keep doing this."

With Wawrinka's fast serve and trademark one-handed backhand both firing, the 25-year-old often found himself given little time to be proactive.

Wawrinka forced his Japanese opponent onto the back-foot by continually pressuring his serve but was not completely flawless, wasting five consecutive match points in the tiebreak.

"I'm still nervous from the end of that tiebreak," said the 2014 champion in his on-court interview. "You have to go for it. I was a little defensive."

He now awaits the winner of the evening match between world No. 1 Novak Djokovic, who Wawrinka dismissed in the quarters last year, and eighth seed Milos Raonic.

Madison Keys responded maturely after treatment to a troublesome left adductor to defeat Venus Williams 6-3, 4-6, 6-4 and set up a semifinal date with her opponent's sister, Serena.

She is the third consecutive 19-year-old woman to make the Australian Open last four after Sloane Stephens and Eugenie Bouchard.

Inspired to play tennis at age four by Venus and sister Serena, Keys forced the seven-time Grand Slam champion into constant errors as she switched risky blasts for more cautious strokes.

"The moment is definitely sweet beating Venus," said the ecstatic American who will jump into the top-20 on Monday.

Venus got away with poor tennis early but Keys soon punished her.

Wayward serving and a ballooning error rate from the five-time Wimbledon champion saw Keys take the initiative by moving into the court and crunching forehands.

The left adductor injury that prematurely ended Keys' 2014 run at Wimbledon flared again in the second set.

But with a calm head, Keys wore down her off-key opponent and resisted the temptation to unleash risky ground strokes.

Venus, already hitting three unforced errors for every winner, allowed Keys to break back in the third set before conceding serve in the match's final game.

Keys will need to be at the top of her game if she is to trouble Serena Williams after the almost-voiceless world No. 1 refused to allow 11th-seeded Dominika Cibulkova into their quarterfinal.

The 160-centimeter Cibulkova was helpless as the women's game's biggest server ruthlessly hit 15 aces and moved the lunging Slovak to the extremities of the court.

"I knew I had to be good today," said the croaky 18-time Grand Slam champion.

Quarterfinal statistics show Keys averaged higher serve and forehand speeds than Serena.

But she will need a remarkable game plan to beat the five-time champion who has never failed to win the title after making the final four at Melbourne Park.

Earlier, China's Zheng Jie and Chinese Taipei's Chan Yung-Jan made the women's doubles final with a 6-3, 6-2 win over Barbora Zahlavova Strycova and Michaella Krajicek. Endi