Top-seeded titleholder Agnieszka Radwanska and former world No 1 Caroline Wozniacki have crashed out on a forgettable day for the drawcards at the Sydney International.

Radwanska slipped up (7-5 6-3) against American qualifier Bethanie Mattek-Sands, marking the first time in the professional era that the women's champion bombed out in the opening match of her trophy defence.

Wozniacki, the sixth seed, followed her out the exit gates later yesterday with a 6-4 7-6 (9-7) loss to Czech Lucie Safarova.

Radwanska insists she can still contend for Australian Open honours despite a worrying shoulder injury and having not won competitive matches since October.

The world No 5 received treatment on her right shoulder during last week's Hopman Cup in Perth and, while loath to blame the injury for her defeat, said it still bothered her.

"Maybe a little bit but I have good painkillers," Radwanska said.

The non-sanctioned Hopman Cup aside, Radwanska hasn't won a set - let alone a match - in more than two months after she lost all three round-robin games at the season-ending championships in Istanbul.

The former Wimbledon runner-up's run of outs is a far cry from last year when she arrived at Melbourne Park for the season's first grand slam on a nine-match winning streak after picking up back-to-back titles in Auckland and Sydney.

The 24-year-old Pole is refusing to panic, claiming three wins at the Hopman Cup is proof enough she's not playing badly.

"Every week is [a] different story. You start over and over again," she said.

AAP