MELBOURNE (AFP) - World No. 1 Rafael Nadal fought off a spirited challenge from Japan's Kei Nishikori to win through to the quarter-finals of the Australian Open today.

The Spaniard won 7-6 (7-3), 7-5, 7-6 (7-3) in three hours and 17 minutes and will play Bulgaria's Grigor Dimitrov in the last eight.

Nishikori, under new coach Michael Chang, pressed Nadal all the way and had his chances to take sets off the top seed.

Nadal, a 13-time Grand Slam champion, showcased his renowned fighting qualities when he won the big points for his sixth win over Nishikori.

"He's a fantastic player and Kei is able to hit the ball very early and the ball was coming back very quick," said Nadal, who is now on a nine-match winning streak.

"It was difficult for me to take position inside the court and I was close to losing every set so I congratulate Kei and I feel he will have a great season."