Radwanska ends Konta's Sydney International defence

Sydney - Former champion Agnieszka Radwanska ended Johanna Konta's Sydney International defence with a 6-3, 7-5 win on Tuesday to advance to the second round.

The fourth-seeded Konta was playing her first match since retiring from her Brisbane International quarterfinal last week with a hip injury. 

Third-seeded and French Open champion Jelena Ostapenko, No 5-seeded Kristina Mladenovic, sixth-seeded US Open winner Sloane Stephens and No 8-seeded Anastasija Sevastova also lost their first-round matches. 

Angelique Kerber was scheduled to play second-seeded Venus Williams later on Tuesday.

Former US Open champion Samantha Stosur won her first-round match, beating Carina Witthoeft 4-6, 7-5, 6-3. 

In men's first-round play, Leonardo Mayer had a 7-5, 6-3 upset win over eighth-seeded Mischa Zverev.