Serena Williams started her fourth decade on the WTA Tour with a straight-set victory over Italian qualifier Camila Giorgi at the Auckland Classic.

The 38-year-old American, playing for the first time since losing in September's US Open final, won 6-3 6-2.

Former world number one Caroline Wozniacki started her final season with a 6-1 6-0 win over Paige Mary Hourigan.

At the Brisbane International, world number four Naomi Osaka beat Greece's Maria Sakkari in three sets.

That extended the 22-year-old Japanese's winning streak to a 12th match, having not lost since her US Open last-16 defeat by Belinda Bencic.