LONDON -- As the sun set on the opening week of Wimbledon, just about the only seeding that truly signified something was No. 1.
That's the number beside the names of Serena Williams and Novak Djokovic, who turned in nearly perfect performances back-to-back Saturday on Centre Court to cap nearly perfect runs to the fourth round at the All England Club, while chaos reigned all around them.
In the final match of the fortnight's first half, played with the roof closed and lights glowing to make sure it would get done as darkness approached, defending champion Williams used eight aces and 11 return winners to power past 42-year-old Kimiko Date-Krumm of Japan 6-2, 6-0 in 61 minutes.
"She didn't lose energy, and her game, I think, is getting better, day after day. Not better in general, but adapting to the surface. Everything is getting better," said French coach Patrick Mouratoglou, who has been working with Williams over the past year, when she is 77-3. "So now let's enter into the most important part of the tournament. ... Now the matches are going to get tougher and tougher."
Might not necessarily have been a fair fight, considering that Date-Krumm is ranked 84th and was the oldest woman to reach the third round at Wimbledon in the 45-year Open era. Never better than a semifinalist at a Grand Slam tournament, she played Williams evenly for about three games, before the 16-time major champion took over.
"She has so much power, speed," Date-Krumm said. "She has everything."
Williams has won all six sets she's played, allowing her opponents a total of 11 games.
"You don't want to play your best tennis in the first round and continue to go down. I feel like I try to play better as each match goes on," said Williams, whose 34-match winning streak is the longest for a woman since older sister Venus had a run of 35 in 2000. "I try to find out something I can improve on from each match so I can do it better in the next round."
In other words: Look out, Sabine Lisicki, the 23rd-seeded German who will meet Williams on Monday for a quarterfinal berth.
How certain was Lisicki that she would be dealing with Williams and not Date-Krumm? Lisicki tweeted a photo of her with Haas early in the second set of Williams' match, writing: "Last Germans standing" and "We both play the no1's next."
Resuming at the start of the third set, the 17th-seeded Stephens fell behind 2-0, but Cetkovska double-faulted three times while letting the American take a 4-3 edge.
Stephens, one of four American women to reach the third round, is in the round of 16 for a third consecutive Grand Slam tournament. At the Australian Open in January, she defeated Williams en route to the semifinals.
There are some fresh faces among the women. That includes 19-year-old Laura Robson, the first British woman to reach Wimbledon's fourth round since 1998; 19-year-old Monica Puig of Puerto Rico; and 20-year-old Sloane Stephens of the U.S., who'll face Puig on Monday.
That matchup prompted this question for Stephens from a reporter: Is there pressure for you when you're playing someone in the next round who you're older than?
"Like a year, OK," Stephens said. "No, not really."
Radwanska, who lost to Williams in last year's final, needed five match points before sealing the victory when Keys sent a return wide. The American had erased four match points in the previous game and finished with 15 aces, but could not muster a comeback against the Pole.
Radwanska reached the fourth round for the sixth time in eight appearances at the All England Club.
"I'm very happy to be a little bit better," Radwanska said. "It was really close. Every set was really tight."
The 18-year-old Keys was making her Wimbledon debut.
Robson also advanced, rallying from a set and a break down and benefiting from a crucial overturned call to beat Marina Erakovic of New Zealand 1-6, 7-5, 6-3.
Erakovic served for the match in the second set, only for Robson to break back. Having then earned a set point at 6-5, Robson barely got a return back that looped high and just caught the edge of the line, but was called out before Erakovic could smack a winner. Robson successfully challenged the call and the point was replayed, with Erakovic double-faulting to hand her opponent the set.
Robson then jumped out to a 4-0 lead in the third set, and clinched the victory with a forehand winner.
At 31, Williams is the oldest No. 1 in WTA rankings history, but she's still more than a decade Date-Krumm's junior.
"I honestly never thought I would play until my 30s, to be honest. I don't see my stopping any time soon," she said. "However, I don't see myself playing into my 40s. That's why I have so much respect for Kimiko."
Williams was rather dominant serving and receiving. In the first set, she delivered seven aces at up to 116 mph, at least one in each of her four services game, and hit nine return winners, at least one in each of Date-Krumm's four service games.
When it was over, Williams wagged an index finger in the air, as if to remind all she is No. 1, then exchanged high-fives with some fans.
"Every time I go out there, I tell you, I feel like anything can happen. I don't feel invincible. I feel like anything can happen," she said. "More than anything, that keeps me completely motivated."
Earlier Saturday, Petra Kvitova avoided becoming the latest former champion to be knocked out in the first week at Wimbledon, rallying from a break down in the final set to beat Ekaterina Makarova of Russia 6-3, 2-6, 6-3.
The match had been halted Friday with Makarova up 2-1 in the third set, but the eighth-seeded Kvitova broke right back when play resumed and won the next two games as well. After losing her own serve, the Czech player broke again for a 5-3 lead and then converted her third match point with a forehand winner.
"It was another day for me," Kvitova said. "I played really well. I should go for every point and play my game. So I played quite aggressively. That was the key."
Kvitova won Wimbledon in 2011 but has struggled to match that performance since and has slipped from second to eighth in the rankings. She has a good chance of reaching her second final at the All England Club, however, having seen second-seeded Victoria Azarenka and former champion Maria Sharapova already eliminated on her side of the draw.
"It's still so far away," Kvitova said. "I'm the highest-ranked player (left) in my half, but there's still a lot of great players over there."
To have a chance at another title, though, Kvitova said her consistency has to improve.
"In 2011 I played really well. I mean, I play my best, for sure. Every shot was going to the court," she said. "It's not the same this year. ... I drop off little bit. It's always little bit up and down, but I hope it will be more up than down."
Because of rain over the last two days, Wimbledon organizers were playing a bit of catch-up with the schedule on Saturday, before Sunday's rest day.
As is traditional on the middle Saturday of the tournament, the Royal Box on Centre Court was filled with a number of invited sports stars, this year mainly British gold-medal winners from the London Olympics. Among those getting the biggest ovation from the crowd were cyclists Chris Hoy and Victoria Pendleton -- as well as Andy Murray, who donned a suit and tie to make a brief appearance in the box to celebrate his singles gold medal won on Centre Court.
Information from The Associated Press was used in this report.