Aus Open PHOTOS: Djokovic downs Nishikori to set up Federer showdown

Images from the matches played on Day 9 at the Australian Open at Melbourne Park on Tuesday

Defending champion Novak Djokovic issued a chilling warning to his Australian Open challengers on Tuesday by storming to a 6-3, 6-2, 6-4 victory over seventh seed Kei Nishikori to set up a blockbuster semi-final against Roger Federer.

The World No 1 was far from his imperious best and struggled on serve but was content to allow his Japanese opponent to fall on his own sword with 54 unforced errors under the Rod Laver Arena floodlights.

Nishikori broke the Serb twice in the third set and edged 3-1 ahead but was unable to capitalise on his own serve and threw his racquet onto the court in a rare show of frustration.

Djokovic fired a sizzling cross-court backhand winner to close out the match and will make his sixth appearance in the last four at MelbournePark, having avenged his loss to Nishikori in the 2014 US Open semi-finals.

Radwanska dispatches Suarez Navarro, to meet Serena in semis

Fourth seed Agnieszka Radwanska advanced to her second Australian Open semi-final after beating Spain's Carla Suarez Navarro 6-1, 6-3 at Rod Laver Arena on Tuesday.

The 26-year-old Pole jumped out to a 4-0 lead with two breaks of serve in the first set, and while the Spaniard finally managed to hold in the fifth game, Radwanska broke again on her second set point to seal it in 28 minutes.

Radwanska opened up a 2-0 lead in the second but then neither player held serve for the next three games until 10th seed Suarez Navarro won an 11-minute sixth game to level at 3-3.

Radwanska, who also made the last four in 2014, broke again in the eighth game before serving out for the match.

She will next meet defending champion Serena Williams.

Serena continues Sharapova dominance

Reigning champion Serena Williams ramped up the power in the second set to vanquish fifth seed Maria Sharapova for the 18th match in a row and reach the semi-finals of the Australian Open with a 6-4, 6-1 victory on Tuesday.

Sharapova broke the world number one in the first game and mounted a stiff challenge in the opening set but wilted in the second to extend a losing record that goes back 12 years.

The 28-year-old Russian, who last beat Williams at the season-ending tour championships in 2004, kept pace with her 34-year-old opponent for all but the last game of the first set, before crumbling in the second.

Federer cruises past Berdych

World No 2 and 17-time Grand Slam champion Roger Federer comfortably accounted for sixth seed Tomas Berdych to move into the Australian Open semi-finals on Monday.

The Swiss legend registered a clinically efficient 7-6(4), 6-2, 6-4 win to put himself in a position to claim his 18th major title.

"It's part of the reason why I guess I'm still playing. I feel like I'm competitive at the top. I can beat all the guys on tour," Federer told reporters.

"It's nice now that in the last three slams that I've been as consistent as I have been."