Serena Williams extended her unbeaten run against Maria Sharapova to 18 matches across 12 years as she eased into the Australian Open semi-final this morning.

The opening set was an even affair and Sharapova could have taken a surprise lead but she squandered two break points in the ninth game, before Williams claimed the winning break on the fourth of four set points in the tenth.

The American required physio treatment ahead of the second set but it was not to show back on court as she broke twice to quickly race into a 5-0 lead.

Sharapova showed some signs of making a comeback in the seventh game with two break points, but Williams's resilience told as she wrapped up the match 6-4 6-1 in just over an hour and a half.

Williams will now go on to face Agnieszka Radwanska in the semi-final as the world number one bids for back-to-back titles in Melbourne.