They are, in terms of sustained excellence, the WTA's power trio. Serena and Venus Williams and Kim Clijsters have won a combined 24 Grand Slam singles titles -- that's more than double the rest of the active field; eight other women have won a total of 11 majors.
But there is a growing downside to all of these accumulated achievements. When Clijsters was asked Wednesday if she was going to play Fed Cup for Belgium in April, she said no.
"Because I'm old," she said smiling, but telling the truth about this body-battering sport. "I have a daughter and a family. We have a tough schedule this summer, so I have to plan my schedule wisely if I want to be able to last throughout the season."
Clijsters turns 29 in June.
The Williams sisters and Clijsters -- whose average age is just north of 30 -- did not play at Indian Wells, but they are all in the field at the Sony Ericsson Open in Key Biscayne, Fla. They came in lightly raced, so to speak, with only 18 matches between them. No. 1-ranked Victoria Azarenka, by contrast, has won all 23 of her matches in 2011.
The biggest questions surround Venus, who hasn't played an official match in more than six months as she has dealt with her energy-depleting Sjogren's syndrome. Her ranking, No. 134, is her lowest-ever at Miami, including for her debut 15 years ago as a 16-year-old.
Venus, who turns 32 in June, came out of the box fast in her first-round match against Japan's Kimiko Date-Krumm, crafting an impressive opening-set bagel and winning 6-0, 6-3. The bad news? She's got No. 3-ranked Petra Kvitova, the reigning Wimbledon champion, in the second round Friday at 7:30 ET and, if she gets that far, ascendant Ana Ivanovic in the fourth.
"While it wouldn't surprise me if Kim and Serena got it together and won a major, if Venus did it, it would be a surprise," ESPN analyst Pam Shriver said. "Frankly, in her comeback she's dealing with more, a tougher hand of cards. She looked OK, like in the first round of [U.S.] Open, and then couldn't lift her arm up because she was so exhausted. There's a lot of unknowns. It's hard to trust her being fit."
Clijsters, too, has struggled with injuries and fitness. She retired from a semifinal match in Brisbane with a stiff left hip and rolled her right ankle in a fourth-round match at the Australian Open. If it hadn't been a major, she acknowledged this week, she would have withdrawn from the tournament. As it was, she soldiered on, beating Caroline Wozniacki in the quarterfinals before pushing the eventual champion, Azarenka, to three sets.
After dropping the first set of her first-round match against Jarmila Gajdosova, Clijsters quickly found her form, winning 4-6, 6-1, 6-0.
"One thing I can count on is I have the experience," she said afterward. "It doesn't take me that long to get used to it again. That's a good thing. It has become tougher. Like today, if I don't improve my level in the second or in the third set, then I could lose this match."
Clijsters has a tough second-round match with No. 14 seed Julia Goerges, but it is not hard to imagine her advancing to the fourth round, where she could meet Wozniacki, the No. 4 seed.
Serena, 30, meets wild card Shuai Zhang in the first round and could draw reigning U.S. Open champion Samantha Stosur in the quarters. Serena injured her left ankle in Brisbane and lost a surprising fourth-round match at the Australian Open to unseeded Ekaterina Makarova -- her first loss in Melbourne in four years.
"I feel like Kim and Serena, barring an ankle turn or a new injury, are still two of most talented players on tour, the ones with the most experience of getting to finals of majors the last few years," Shriver observed. "One of them could win a major, but I'm nowhere near as sure as I was in December before Azarenka took off on this Djokovic-like start to the season."
As usual, when questioned closely, Venus did not volunteer much concrete information.
"I do have experience on my side," she said after the Date-Krumm match, "but of course it can go any way. Just to be here in this tournament is a huge win for me, just to get back to this level.
"I feel like a person that has an autoimmune disease. I'm not going to probably feel like everybody else."
Is she confident she can get through the tournament?
"I'm confident I will give 110 percent," she answered coyly. "My goal is to peak for the Olympics. I know how to play, so I haven't lost any steam in the fact that I can play tennis."
It's an odd time in women's tennis. There are a slew of young players -- Azarenka, Kvitova, Wozniacki and Agnieszka Radwanska -- asserting themselves, while the power trio, joined by middle-agers Maria Sharapova and Stosur, clearly are still viable major champions.
"I keep waiting for the full house in women's tennis," Shriver said. "Everybody to be back and healthy. Maybe we'll get a glimpse in Miami. We've had some teasing where you think they're back, but something happens and somebody disappears again.
"It would be nice if for six months -- the French Open, Wimbledon, the Olympics and the U.S. Open -- if these old players and young power were playing each other. It would be quite a nice mix."