Andrea Petkovic’s hip-shaking shuffle—the Petko dance—has become tennis’ most distinctive celebration since Andrew Ilie’s shirt-shredding revelry. Today, Petkovic gave Caroline Wozniacki little wiggle room in high-stepping past the top seed, 7-5, 3-6, 6-3.

A weary Wozniacki saw her eight-match winning streak come to an end as Petkovic became the first German woman to beat a reigning world No. 1 since Steffi Graf rallied past Martina Hingis in the 1999 French Open final, and the first to reach the Miami quarters since Anke Huber in 2001.

It was not a consistently high-quality match: Wozniacki committed more than 50 unforced errors, converted just five of 17 break-point chances and squandered three set points on Petkovic’s serve at 5-4 in the first set. But credit Petkovic—who can rip the ball off both wings one minute and spray her spasmodic forehand with a mind-numbing lack of conscience the next—with keeping her cool in serving out her biggest career win at love, punctuating the two hour, 24-minute match with a stinging ace out wide.

“I didn’t try to overpower her because she’s so good at bringing the ball back, so I tried to mix it up a little bit,” Petkovic told Tennis Channel.

Wozniacki was bidding to join Graf and Kim Clijsters as the third woman to win Indian Wells and Key Biscayne in succession, but looked a half-step slow and frequently misfired on her forehand.

Neither woman was imposing on serve in an opening set that featured four breaks in the first six games. Serving at 3-4, Petkovic fought off triple break point to hold. Two games later, Wozniacki whipped a backhand down the line for double set point. Petkovic saved the first with a backhand winner, also down the line, and the second when Wozniacki shanked a mid-court forehand. Withstanding a third set point, Petkovic survived a series of cross-court backhands, then snapped one of her own to pass Wozniacki and hold for 5-all; a furious fist pump ensued. Petkovic broke at 15 and sealed the first set, singeing the sideline with her first ace.

Undeterred, Wozniacki won three straight games to close out the second set, only to see Petkovic seize a 2-0 lead to start the third. Wozniacki’s second serve is her biggest weakness—she often spun sub-80 mph second serves into the box today—and Petkovic stepped inside the baseline to pound them. She did so with a backhand to break for 4-2, and consolidated at 30 when Wozniacki smothered a forehand into net.

An explosive player and spunky personality, Petkovic has a slight hitch on her serve, but none of that mattered much as she served out the match at love and unleashed her distinctive dance to celebrate. Can she choreograph another upset? Petkovic may face 2010 Indian Wells champ Jelena Jankovic, who plays Anabel Medina Garrigues next, for a spot in the final four.

—Richard Pagliaro