Williams was not at her blistering best, with her forehand and first serve both well below par, but it is ominous for the rest of the draw that there is still so much more to come. "She's an incredibly intense, focused player who was No 1 and has won so many Grand Slams for a reason".

"Playing someone like that you have to play with fire and intensity".

Roger Federer advanced to his 39th Grand Slam semifinal, beating Tomas Berdych 7-6 (4), 6-2, 6-4.

He's now the oldest man since 1979 (Colin Dibley) to reach the Australian Open semis, where he'll play either five-time champion Novak Djokovic or No. 7 Kei Nishikori. "I still have to win two matches against potentially two extremely tough opponents".

Radwanska, who is from Poland, has never won a major title.

Top seed Serena Williams withstood a tense first set and a late match charge to take out Maria Sharapova, defeating the No. 5 seed for an 18th straight time, 6-4, 6-1.

"I think if you're serving maybe 180 against somebody else compared to Serena, that's an ace", Sharapova said after the match when asked about her serves.

"She's been playing really well towards the end of the year, and already this year she's been very consistent", Williams said of the Pole, a friend off court.

When she needed it most, however, facing four set points in the crucial 10th game of the match, her serve failed her and she ceded the opening stanza 6-4.

Serena Williams, with 21 Grand Slam titles in her trophy cabinet, thinks she has nothing left to prove to anyone and just wants to have fun for the remainder of her career.

Maria Sharapova broke Serena Williams's serve to open the match and stuck with her through the next seven games.

A similar player-Roberta Vinci-ended Williams' run at the 2015 US Open last summer with the calendar Grand Slam on the line.

You really do have to feel for a lot of the top tennis players who have been around for the past few years, as they have barely been given a sniff of winning the big tournaments, thanks to the dominance of the world number one Serena Williams. "I'm happy to have that and I'll be ready for the semi", she said.

Williams said the Russian brings out the best in her. "When I play her, I know automatically I have to step up my game", she said.

"Right now I have nothing to lose", Radwanska said. "She is very solid, like most Spanish players and I knew everything would come back to my side".

Ahead of the Williams-Sharapova showdown, Radwanska, a semi-finalist previous year, said she did not mind who she faced in the last-four clash on Thursday. Federer is considered to be a serious opponent to play against Djokovic.

Afterward, the 21-time Grand Slam singles champion tried to explain why she's been so successful against such a unsafe foe, as noted by Christopher Clarey of the New York Times.

To reach her 22nd title, she'll first have to get past No. 4 Agnieszka Radwanska in the semi-final.

After the match, the Serb was asked about his 45th meeting with Federer, saying: "We keep playing each other in almost every big tournament".