Serena Williams beats Petra Kvitova in Wimbledon quarters

Serena Williams beat defending champion Petra Kvitova in straight sets to reach the Wimbledon semi-finals.

While rain fell at SW19, the American sixth seed produced a series of punishing winners to defeat the Czech 6-3 7-5 under the Centre Court roof.

The four-time champion will play Victoria Azarenka next after the second seed beat Tamira Paszek 6-3 7-6 (7-4).

Eighth seed Angelique Kerber was a 6-3 6-7 (7-9) 7-5 winner over Sabine Lisicki in the all German clash.

Kerber will play third seed Agnieszka Radwanska, who beat 17th seed Maria Kirilenko 7-5 4-6 7-5.

Williams told BBC Sport that she had the "time of her life" in what was her first match under the roof.

"I had to step it up today because I was playing the defending champion, it was tough," said the 30-year-old.

"It's exciting. Everyone thinks about lifting the trophy. It's something I've thought about, but my main goal is to keep progressing.

"If I want to win the title, I have to step it up. There are a lot of people vying for it. I'm happy just to be in the tournament."

Kvitova had not lost at Wimbledon since being beaten by Williams in the 2010 semi-finals, but was blasted off court by the 13-time Grand Slam champion, who sent down 13 aces and had an 86% first-serve success rate.

Once Williams recovered from serving at 30-0 down in the opening game of the match she barely looked back, sealing the break she needed to take the first set in the sixth.

Kvitova improved in the second set, finding lines with regularity and forcing a set point in the 10th game.

But after the fourth seed netted with a routine one-hander, Williams forced a decisive break in the next game and served out for victory.

Azarenka broke her unseeded opponent at 4-3 before serving out the first set, the Belarusian bullying her Austrian rival at times.

She served for the match at 5-4 and 6-5 in the second set only to be broken on both occasions, her serve having been rock-solid until then.

But the 21-year-old Paszek's commendable resolve was finally ground down in the tie-breaker, Azarenka prevailing 7-4.

Lisicki, who knocked out Maria Sharapova in the fourth round, saved three match points in the second set and served for the match at 5-3 in the third.

But Kerber, 24, bounced back to win the last four games, finally converting her fifth match point when Lisicki sent a backhand wide.

Afterwards, Kerber said it was difficult playing against someone she has known since they were children.

"We've known each other from a young age and it was mentally not easy," admitted Kerber after reaching the semi-finals at SW19 for the first time.

"It doesn't matter who you play out there. You need to play your best. I stuck to my plan and I think I did a great job."

The match between Radwanska and Kirilenko started on Court One but was suspended because of rain, with the deciding set going with serve at 4-4.

Initially it was announced the match would be finished on Wednesday but it was unexpectedly switched to Centre Court and restarted at roughly 2130.

And Radwanska it was who felt the benefit of an extended break, breaking her Russian opponent and wrapping up the match in barely 15 minutes.