Kim Clijsters, playing her final Wimbledon before retirement, said she believes she can knock out the top seeds despite having gone through 14 months of injury hell.
The unseeded Belgian, a four-time Grand Slam winner and a Wimbledon semi-finalist in 2003, beat Serbian 18th seed Jelena Jankovic 6-2, 6-4 in one of the big clashes of the first round.
Clijsters, a former world number one, had come into the tournament under an injury cloud.
A stomach strain had caused the 29-year-old to pull out of her 's-Hertogenbosch semi-final at the weekend in what was her first event since March.
But the world number 47, who will retire for a second and final time after the US Open, was untroubled against the error-plagued, former world number one Jankovic who lost in the first round for a second successive year.
"If I'm healthy and I'm playing my best tennis I believe that I can beat a lot of the top players here, but it's a matter of trying to achieve that every match," Clijsters said.
The last 14 months have been an unhappy time on the court for Clijsters, with injuries repeatedly halting her progress.
"There were definitely moments where it was hard and where I thought, should I retire now? Maybe my body is saying it's enough and this second career has been good and maybe I should just accept that," she said.
"But then again after a couple days I felt like, no, I want to do the rehab and refocus.
"Unfortunately, when one injury got better, another popped up
"I've played some of my best tennis in the last year and a half or so. That's unfortunate, because I haven't been able to show that in tournaments."
She said knowing that she will retire within months means she is taking the chance to soak up the Wimbledon experience for a final time.
"This is definitely going to be it, so I take everything in. Whether I'm practicing on one of the practice courts out here, I look around and I take it in. So it's more emotional, definitely," she said.
"I have a lot of nostalgic emotions and feelings. When I get off at the train station and I go to Wimbledon, it's a very special, special place for me."
Clijsters said she will have an ultrasound scan every two days during Wimbledon to check that her muscle tear is not getting worse.
She will face Andrea Hlavackova of the Czech Republic for a place in the round of 32.