Wimbledon (AP) -- Thanks to a bit of advice from her big sister and a bunch of aces from her big serve, Serena Williams is back in the Wimbledon semifinals.

With two more victories, Williams will be holding a Grand Slam trophy for the first time in two years.

The thud of racket-against-ball reverberating under the closed Centre Court roof, Williams smacked 13 aces at up to 120 mph and overpowered defending champion Petra Kvitova 6-3, 7-5 in the quarterfinals Tuesday at the All England Club.

Beforehand, Williams' father and coach, Richard, asked his other title-winning daughter to relay some suggestions.

"I went and had Venus talk to her, because Venus can get (through) to Serena better than anyone in the world. So I told Venus, `I'm not going to talk to her. You talk to her.' So Venus went and talked to her. When the match was over, I told her, `Venus: Good coaching! Good coaching!"' Dad said after snapping photos of Serena's victory from his front-row perch in the guest box above a scoreboard.

"I wanted Serena to move her feet a little bit more and to not concentrate on what the girl's doing, but concentrate exactly on what she wished to do," he continued. "And that was the only message."

Consider it delivered.

The 30-year-old Williams, bidding to become the first woman at least that age to win a major title since Martina Navratilova at Wimbledon in 1990, turned in her best performance of the tournament against her most difficult opponent. After being stretched to 9-7 and 7-5 third sets against less-accomplished women in the two previous rounds, the No. 6-seeded Williams was on top of things from the get-go against No. 4 Kvitova.

"You can't play a defending Wimbledon champion or Grand Slam champion and not elevate your game," said Williams, who produced 27 winners and only 10 unforced errors. "I had to weed out the riffraff and just get serious."

Kvitova had won 16 of her last 17 matches at Wimbledon, including 11 in a row since a loss to Williams in the 2010 semifinals. Two days later, Williams went on to win the championship - her fourth at Wimbledon, her 13th at a Grand Slam tournament and her most recent to date.

Within a week, Williams cut her feet on glass at a restaurant, leading to a series of health problems, including being hospitalized for clots in her lungs, then the removal of a pocket of blood under the skin on her stomach.

"No one tries to have ups and downs. Some things happen sometimes, and you have absolutely no control over it," said Williams, whose only first-round loss in 48 Grand Slam tournaments came at the French Open in late May. "So I think it's how you recover from that, and how you handle the downs even more than the ups can really (reveal your) character."

On Thursday, Williams will play No. 2 Victoria Azarenka of Belarus, the reigning Australian Open champion, who defeated unseeded Tamira Paszek 6-3, 7-6 (4) under the roof at night to reach the Wimbledon semifinals for the second straight year. The other semifinal will be No. 3 Agnieszka Radwanska of Poland against No. 8 Angelique Kerber of Germany.

A little before 10 p.m. on Centre Court, Radwanska finished her 7-5, 4-6, 7-5 victory over No. 17 Maria Kirilenko - whose boyfriend, two-time NHL MVP Alex Ovechkin of the Washington Capitals, was in the stands. Earlier, the match was forced off Court 1 because of showers, tied 4-all in the third set.

"Today was for me, like, 40 hours," Radwanska said after reaching her first Grand Slam semifinal. "I was on and off all the time, waiting pretty much all day."

Kerber was a 6-3, 6-7 (7), 7-5 winner over No. 15 Sabine Lisicki in an all-German matchup. Lisicki saved three match points in the second set, but then let a 5-3 lead slip away in the third against Kerber, also a semifinalist at last year's U.S. Open.

Williams owns, by far, the best resume of any woman in action Tuesday. She was participating in her 33rd major quarterfinal; the other seven players have been in a total of 29.

Not surprisingly, Kvitova expects Williams to win the title.

Asked how difficult it is for anyone to beat Williams when she plays the way she did Tuesday, the Czech replied: "It is big difficult."

Impossible?

"I can't say `impossible.' She's human," Kvitova said.

Both played impressive grass-court tennis, hitting powerfully, serving well and returning dangerously. Williams simply was superior doing all of it.

After losing the first two points of the match, Williams buckled down and took 20 of 23 on her serve in the rest of that set. Kvitova hung tough in the second, though, yelping louder to punctuate winners. Then came a key moment, with Kvitova ahead 5-4 and Williams serving at 30-all. Kvitova whipped a cross-court backhand winner to earn her only break point of the day.

But Williams delivered a 109 mph serve, and Kvitova's backhand return slapped against the net's white tape. From there, Kvitova shanked a forehand off her frame, and Williams hit a volley winner after both wound up at the net.

In the next game, with Kvitova serving at 5-all, 30-love, she fell apart, making four consecutive miscues. The last, which gave Williams a break and a 6-5 lead, was the most egregious, a forehand into the net off a floated return.

That gave Williams a chance to serve it out. Did she ever. The four points she won, each serve loud on impact: 117 mph ace, 117 mph ace, 116 mph ace, 113 mph service winner.

"I loved the sound. It was really cool. I've never played under the roof," Williams said. "It's kind of like a `whoosh' and a `pop.' ... It's almost like a video game, but you're playing. It kind of flies through and you hear it when it lands."

With more rain in the forecast, the roof could be shut again Wednesday, when the men's quarterfinals are No. 1 Novak Djokovic vs. No. 31 Florian Mayer, No. 3 Roger Federer vs. Mikhail Youzhny, No. 4 Andy Murray vs. No. 7 David Ferrer, and No. 5 Jo-Wilfried Tsonga vs. No. 27 Philipp Kohlschreiber.

While defending champion Djokovic, six-time champion Federer and Youzhny got a chance to rest Tuesday - particularly important for Federer, whose back ached during his fourth-round victory - everyone else slogged through a start-stop-start-stop afternoon of rain delays with the temperature in the low 60s.

The last two American men in the draw were beaten: 10th-seeded Mardy Fish wasted the one-set lead he built before play was suspended Monday and lost to Tsonga 4-6, 7-6 (4), 6-4, 6-4, and 126th-ranked qualifier Brian Baker's surprising run ended against Kohlschreiber 6-1, 7-6 (4), 6-3.

"I went to bed last night, and I thought I could maybe win the tournament, the way I was playing," said Fish, who hadn't played a match in 2 1/2 months before Wimbledon because of an accelerated heartbeat.

Murray eliminated No. 16 Marin Cilic 7-5, 6-2, 6-3 to prolong Britain's hopes for its first male champion at Wimbledon since 1936; Ferrer easily got past No. 9 Juan Martin del Potro 6-3, 6-2, 6-3 to earn his debut trip to the quarterfinals at the All England Club; Mayer defeated No. 18 Richard Gasquet 6-3, 6-1, 3-6, 6-2 to return to the round of eight for the first time since 2004.

"I can play everything. I can play serve-and-volley. I can play drop shots. I can play with slice. I can play fast. So I will try to irritate him, maybe, a little bit," Mayer said about Djokovic. "You never know in tennis. Everything is possible."