Serena Williams of the US reacts after a point against Switzerland's Belinda Bencic during their women's singles match on day two of the Australian Open tennis tournament in Melbourne on January 17, 2017. Pic/AFP

Melbourne: Serena Williams launched her bid for a 23rd grand slam title with a 6-4 6-3 win over Belinda Bencic at the Australian Open on Tuesday, swatting aside doubts over her fitness and motivation on a sweltering day at Melbourne Park.