Serena Williams overcame a sluggish start to win her opening match of the new season in Perth Monday, two weeks out from 2019's first Grand Slam.

The 37-year-old was a long way off her commanding best and was visibly frustrated with her own game early in her Hopman Cup singles match, but still did enough to beat Greece's Maria Sakkari in straight sets.

However, it was Sakkari and her team-mate Stefanos Tsitsipas who had the last laugh as Greece beat the USA 2-1 in the mixed doubles Group B tie.

In her first tournament outing since the controversial loss to Naomi Osaka in the US Open final in September, Williams struggled early and her groundstrokes were erratic in the first set.

Sakkari, ranked 41st in the world, gained an early break and served for the first set but couldn't capitalise despite several gilt-edged opportunities.

That opened the door for Williams, the bookmakers' favourite for the upcoming Australian Open in Melbourne, to power back and ultimately win 7-6 (7/3), 6-2 in an hour and 44 minutes.

Williams had her left ankle worked on at the end of the first set but it didn't stop her dominating the second, in which she looked more like the player who has won 23 Grand Slam singles titles.