Radwanska suffers Sydney shock, Hewitt out of Kooyong
The world number five, who had won the Sydney title last year as part of a 13-match unbeaten streak that ended in the Australian Open quarter-finals, was upset 7-5 6-2 by the American qualifier in the first match on the main court.
It was the first time the women`s champion had been defeated in her opening match at the tournament since 1990.
Radwanska had a poor end to the season in 2013, losing all three round robin matches at the WTA championships though she won all three matches at the Hopman Cup in Perth last week to give her some impetus heading into Melbourne Park.
The Pole was given a bye in the first round.
Mattek-Sands will now face with either fellow American Madison Keys or Croatian wildcard Ajla Tomljanovic in the quarter-finals.
Danish sixth seed Caroline Wozniacki, who has emerged as a potential title favourite after the in-form Jelena Jankovic lost in the first round on Monday, plays Lucie Safarova later on Tuesday.
The winner of that clash will face either Christina McHale or former Wimbledon champion Petra Kvitova in the quarter-finals.
Fellow former Wimbledon champion Lleyton Hewitt, however, disappointed Kooyong Classic fans with his decision to withdraw from the invitational tournament in Melbourne.
The 32-year-old caused a major upset at the Brisbane International defeating Roger Federer in the final on Sunday and the Australian said he felt he would need the week off to recover properly for the season-opening grand slam.
"At the moment it`s just all about recovery for me," Hewitt told reporters at Kooyong on Tuesday. "When you get older it gets a bit tougher than when you were 16.
"Saturday and Sunday, (there were) brutal conditions up in Brisbane, very little breeze whatsoever, very hot and humid.
"We`re going into the first major and you`ve got to do what`s absolutely right for you."
His place in the eight-man invitational field will be taken by Australian teenager Jordan Thompson, though Hewitt will still play an exhibition match against Wimbledon champion Andy Murray at the Kooyong club on Friday instead.
Reuters ---------------------- ZEENEWS.com