American top seed Serena Williams blitzed into the Australian Open semi-finals with a 6-2, 6-2 demolition of last year's finalist Dominika Cibulkova on Wednesday.

The 18-time Grand Slam champion crushed the 11th seed in 65 minutes to set up a clash with unseeded compatriot Madison Keys in the 26th Grand Slam semi-final of her career.

Williams has made the final four at Melbourne Park five times previously and gone on to win the title every time.

"I knew that I had to beat her today because she was in the final and she plays really well on this court, so I'm really happy to go through," said the 33-year-old, who could barely talk after battling a cough during the tournament.

Fired up after seeing sister Venus lose her quarter-final to Keys, Williams blasted down 15 aces against the hapless Cibulkova, including a 199 kph (124 mph) thunderbolt that left the so-called "pocket rocket" reeling.

The world number one looked focused from the outset and avoided the sluggish starts that marred her earlier matches.

Cibulkova, who went into the match with a 4-0 losing record against Williams, began nervously with two double faults in the opening game, managing to cling on to hold serve.

But Williams effortlessly broke Cibulkova in the second and fourth games, pouncing on the Slovak's weak second serve and giving her opponent no chances during her own service games.

She cracked down eight aces in the first set, including three in the final game to go up 6-2 after 28 minutes.

The massacre continued in the second set, as Williams broke in the opening game and never looked back.