Serena Williams has returned to competitive action for the first time since her controversial defeat in the US Open final, but was unable to prevent the US from slipping to defeat against Greece at the Hopman Cup.

Williams took to the court in Perth, Australia, defeating Maria Sakkari of Greece in straight sets, 7-6(3) 6-2, in their singles game.

However, US pair Williams and Frances Tafoe later fell to defeat in the mixed doubles against the Greeks.

That result, coupled with Tiafoe’s loss in his singles match, meant the US lost the tie 2-1.

The Hopman Cup pits nations against each other in a round-robin group stage format before the group winners meet in Saturday’s final.

Each tie between the nations involves a singles encounter between male and female players before a mixed doubles meeting.

The US’ next clash is against Switzerland on Tuesday, and will pit Swiss legend Roger Federer and Williams against each other in a highly-anticipated mixed doubles clash. The pair have an incredible 43 Grand Slam singles titles between them.

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Williams recently played an exhibition game against sister Venus in Abu Dhabi, but is playing competitively for the first time in Perth since her US Open final defeat to Naomi Osaka in September.

That match was overshadowed by Williams’ furious bust-up with umpire Carlos Ramos, whom she branded a “liar” and “thief” after he issued her with code violations. (RT)