Serena Williams beat Maria Sharapova for the 18th time in a row to reach the Australian Open semi-finals. The defending champion, seeded number one and chasing a 22nd Grand Slam title, saw off fifth seed Sharapova 6-4 6-1 at Melbourne Park. The world number one, who has not lost to Sharapova in 12 years, now faces fourth seed Agnieszka Radwanska. Williams extends dominance over Sharapova Sharapova made it a real contest for almost an hour but eventually buckled under the American's power. Williams, 34, appeared to struggle with her ball toss in the morning sunshine on Rod Laver Arena as she fell 2-0 down. The intensity ratcheted up as the set progressed, with both players repeatedly yelling ""Come on!"" as they tried to grab the initiative. Sharapova, 28, held on valiantly in an eight-minute game to claw her way back to 4-4, but the pressure told in game 10 and Williams clinched the set at the fourth opportunity with a volley. The world number one called for the doctor at the changeover but powered on stronger than ever in the second set, making it 12 games out of 15 as she sealed victory after one hour and 32 minutes. ""It was super intense,"" said Williams. ""She's an incredibly intense and focused player who was world number one. ""When you're playing someone so great you have to come out with a lot of fire and intensity."" Sharapova was equally effusive about Williams. ""She's at a different level. She makes you work. That's inspiring.""