Wimbledon, England ? Novak Djokovic was upset in straight sets by Marat Safin in the second round Wednesday, ending the Serb’s chances of testing his theory about Roger Federer’s vulnerability at Wimbledon.

The 75th-ranked Safin won, 6-4, 7-6 (3), 6-2, on Centre Court. It was a stunning loss for the third-ranked Djokovic, who came to the All England Club confident after beating top-ranked Federer in the semifinals at this year’s Australian Open en route to his first Grand Slam tournament title.

Top-ranked Federer only had a minor hiccup – dropping serve once, the first time since Roland Garros – before getting past Robin Soderling, 6-3, 6-4, 7-6 (3), to extend his streak on grass to 61 matches. The Swiss star looked anything but vulnerable as he continued his bid for a sixth straight Wimbledon title.

Women’s No. 1 Ana Ivanovic, another Serb, struggled but won. The French Open champion saved two match points – including one that bounced off the net chord for a winner – in the second set before overcoming 29-year-old Frenchwoman Nathalie Dechy, 6-7 (2), 7-6 (3), 10-8.

Two-time champion Serena Williams had less trouble, advancing 6-4, 6-4 over Urszula Radwanska on Court 2, called the “graveyard of champions” for its history of upsets.