BAD news for the remainder of the field in the ladies singles.

Serena Williams just got serious.

The bill for the last eight was topped yesterday by the four-time champion's meeting with Petra Kvitova, last year's winner, but when the 30-year-old from Palm Beach Gardens, Florida, is on this kind of form her opponent is usually rendered something of an irrelevance.

Although Kvitova squandered a set point to prolong matters into a decider, this was Williams at her brutal, brilliant best. It was Serena's most convincing display of the tournament and the numbers told the story: the match was decided in her favour by a 6-3, 7-5 scoreline in just one hour and 24 minutes, with another 13 aces taking her total for the tournament to 61, which is more than twice as many as anyone else left in the competition.

With possibly another two matches to play, she is closing in on the 89 she hit at SW19 in 2010, which is a modern record. Seven grand slams have come and gone since Serena last lifted a major trophy, and she came into the tournament on the back of a fourth-round departure in Australia and a shock first round exit in France, but normal service, you might say, has been resumed.

"You can't play a Wimbledon champion or grand slam champion and not elevate your game," said Williams, apparently motivated by a good old talk from her dad, Richard. "I had to weed out the riff raff and just get serious."

The Williams parable requires little pre-amble, but suffice to say that her fifth Wimbledon title would be a fitting conclusion to the player's wilderness years which have seen her suffer from numerous ailments, including a pulmonary embolism last March.

"Obviously no one tries to have ups and downs," Serena said. "Some things happen sometimes and you have absolutely no control over it. So I think it's how you recover from that and how you handle the downs even more than the ups can judge you as a character."

Having dethroned the champion to reach her 21st semi-final in the last 48 grand slams, she becomes a clear favourite to claim her fifth Wimbledon crown on Saturday. "I still have hopefully two more matches to play and win," she said.

For Kvitova, it was at least partial consolation that her opponent had been in such inspired form. Williams had also been responsible for the Czech's last defeat here, in the 2010 semi-final. "It is big difficult [to beat her]," said the Czech. "But I can't say impossible. She's human. But she knows what to do in the important points – that is why she's the great champion. She had a big serve again. I still have a trophy at home, so I'm still happy. But unfortunately I have to leave this tournament in the quarters."

The support act was the all-German grudge match between Sabine Lisicki and Angelique Kerber, the first time since 1987 (and only the second time ever in the Open era) that two Germans had reached the quarter-finals here.

Lisicki, last year's semi-finalist, had toppled Maria Sharapova on Monday but that had only served to steal some of the thunder from her countrywoman. Kerber, who came from nowhere to reach last year's US Open semi-final, has won 44 matches on the LTA tour this year, more than any other player, and had prevailed on all four previous occasions when the players had met.

Over two and a half hours, the two Germans – both of Polish extraction – took part in a wild, topsy-turvy encounter which mesmerised the crowd huddled under the Centre Court roof. Both had served for the set and failed before Kerber held her nerve to close out a 6-3, 6-7 (7), 7-5 victory.

Things might have been rather easier for her had she capitalised on one of the four match points during the second set. The turning point of sorts came when she finally won a Hawk Eye challenge at 0-15 as she served to stay in the tournament, flinging her arms to the sky in faux adulation.

"I think the challenge in the third set where I was serving at 4-5, that was the change," Kerber said. "I think that saved my life in this match. I had 20 or so challenges and this was the first one which was right."

Kerber goes on to face Agnieszka Radwanska in the semi-final, meaning a first time grand slam finalist is guaranteed. It will be a first grand slam semi-final for Radwanska – currently the world No.3, although either she or Viktoria Azarenka will take over as world No.1 on Monday – not to mention giving her the kudos of being the first Polish girl in the Open era to get that far. Her rain-affected semi-final, which began on Court No.1, stood at 7-5, 4-6, 4-4 when it was moved to Centre Court at 9.30pm, something of a surprise considering the All England Club's Andy Murray-related promise that they couldn't move matches once they have started. After saving two match points, the Pole saw out the final set 7-5.

Also playing to a finish at Wimbledon yesterday was Tamira Paszek, who had profited from a similar Kerber wobble at match point to take the grass court title at Eastbourne a fortnight ago.

Her match with Azarenka was also moved to Centre Court, but after twin Belarusian misfires while serving for the match, the world No.2 saw out a laboured 6-3, 7-6 (7-4) win. She proceeds directly to a semi-final showdown with Williams. On yesterday's form, she will have her work cut out.