Daunting return of Venus and Serena

EASTBOURNE, England -- The revolving door at the top of women's tennis continues to spin. Kim Clijsters is out of Wimbledon, but the Williamses are back and picking up right where they left off. Venus Williams hadn't played since retiring at the Australian Open against Andrea Petkovic in January with an abdominal injury. Making her return in Eastbourne this week, Venus was drawn to play Petkovic again, this time winning in three tight sets.

"It was a tough match for her, because I'm kind of a floater right now," Venus said after the match. "That was a little bit of bad luck for her, but for me it was a great opportunity. It felt fitting I guess in a way. It was just very ironic. It was just a great way to start it all off.

After following up with a solid win over Ana Ivanovic in the second round, the elder Williams is within reaching distance of the form that was making her an emerging contender at the Australian Open before injury intervened.

Younger sister Serena is returning to Eastbourne as well, having spent nearly a year away thanks to the injury saga that began when she stepped on glass at a nightclub in Germany shortly after defeating Vera Zvonareva in the Wimbledon final last year. The cuts required two surgeries last season and triggered a life-threatening pulmonary embolism in February, putting her career on the backburner.

"This is totally different from any other comeback, because this has given me a new perspective on my career and [I'm] not taking things for granted," Serena told reporters at the beginning of the week. "There were times when I'm like, 'Oh, another match. This is so hard.' But now it's more like, 'Yes, I'm out here, and I could have had a chance of never being out here again. And especially beginning at the top of your game, having to have something like that happen randomly."

Her opener was all about shaking off the rust, with Serena dropping the first five games in ugly fashion before scratching out a three-set win. Her first proper outing came in the second round against who else but Zvonareva -- a repeat of last year's Wimbledon final. Overnight, she lifted her form several notches, moving with speed and purpose and hitting out on her backhand instead of often slicing it. She looked to be on her way to a straight-sets win when she led 5-3 in the second set, but allowed the Russian back into the match and eventually fell in a three-hour, three-set battle.

"It was a good two matches for me. I couldn't be happier with the amount of tennis that I've played," Serena said afterward. "I feel like I was able to stay out there two hours [Tuesday] and come right back and do a pretty tough three hours today.

"I haven't played in almost a year, so I'm a little sore. It's good I'm sore now, because hopefully next week I won't be as sore.

"One or two points, I could have won the match," she added. "I think that's just me not playing and not actually even holding a racket for over eight months, so it's not overly disappointing.

"I definitely think I can do better, but that's what's so comforting is the fact that I know I can do so much better and I can improve."

When news of Serena's condition first broke, comparisons with other athletes suggested she could be out for much longer. Treatment usually involves blood thinners, which increases the risk of internal bleeding and means patients are advised to avoid activities with risk of falling or violent physical contact. Williams went to hospital after suffering bleeding under the skin in early March.

But a stumble and fall in the last game of her first-round match against Tsvetana Pironkova did not seem to cause her any great alarm, though she paused to recover and received a time warning soon after. There was another tumble at the end of the second set against Zvonareva. Asked if she had been advised to avoid such incidents, Serena made light of the issue, joking, "Look, I always try not to fall down. It's definitely not cool on my nails if I fall, because I can potentially break one, and that makes me really upset."

Her agent, Jill Smoller, said there were no concerns. "It depends what your course of treatment was," she said. "There's no danger with her falling."

At this stage, Venus looks to be readier to make a title run at Wimbledon, but Serena could easily work her way into form if she gets through her first few matches.

Few other players would be given much chance of pulling off a win in such conditions. Kim Clijsters struggled to return after injuring her foot before the French Open, falling. Maria Sharapova has taken the better part of two years to rediscover her form after shoulder surgery. Justine Henin has come the closest to pulling off a Williams-style comeback, making the final of the Australian Open after an 18-month retirement but finding it difficult to keep up the pace in the months that followed. But the sisters, particularly Serena, have pulled it off time and time again, lifting their form for the biggest events.

How do they do it? A few reasons:

1. Self-belief

"I always come out to win, no matter what match, no matter what circumstances," Venus said this week. Serena declared that her goal is to "win seven matches at Wimbledon."

No other players take the court with such self-belief against any and all players, particularly when those other players are facing the Williamses. It gives the sisters a vital mental edge in key moments. And once they hit a good level, they rarely look back.

2. Athleticism

Most players aren't sharp when they come back, and pay the price. But the Williamses are so athletic that they can leap, bound and muscle their way into the points, making up for any rust in their strokes.

3. Power

Unlike most players, both sisters have big serves that prevent opponents from going on the offensive, and their power off the ground also lets them dictate most rallies. Few can handle it well enough to probe any weaknesses that might be lingering early in their comebacks. It's usually the sisters' own errors that contribute heavily to their downfall.

Returning on grass, their strongest surface relative to the rest of the field, increases their chance of success. A Williams has won Wimbledon in nine of the past 11 years.

The seeding committee at Wimbledon obviously agrees, adjusting the women's seeds to move Serena up to No. 8 and Venus up to No. 24. Their current rankings are No. 26 and No. 32, respectively. The bookmakers rate them even higher -- only Maria Sharapova's odds of winning were rated higher than the sisters, and that was before both showed flashes of dangerous potential at Eastbourne.

Still, danger lurks from the early rounds in Grand Slams these days, so the toughest challenge for both will be staying solid and avoiding lapses like the kind that led to Serena's collapse against Zvonareva at Eastbourne.

Given that Venus turns 31 and Serena has only been hitting for a month after her health problems, a Wimbledon victory for either in two weeks' time would probably rate as the biggest comeback in a lengthy history of comebacks.

And as so often in the past, they are setting out together. "I feel like we've been on a similar road together," Serena said. "Her road hasn't been as arduous or as long as mine, but I know what she's been through coming back from Australia. She never retires, and she had to retire. When you're down and someone's down with you, it kind of makes you feel a little better.

"We've been really enjoying our time just getting back together and practicing next to her and seeing her play so well."

The rest of the field, meanwhile, is watching warily.

Kamakshi Tandon is a freelance tennis writer for ESPN.com.