PARIS – World No 1 tennis player Serena Williams has bolstered her position atop the WTA world rankings after winning the Australian Open on Saturday.The 33-year-old American defeated Maria Sharapova in straight sets for her sixth Grand Slam title in Melbourne and 19th in all.Williams is over 1,500 points clear of the Russian who in turn is well ahead of third placed SimonaHalep of Romania.One of the biggest movers of the week was Serena’s older sister Venus. The former world number one reached the last eight in Melbourne for her first Grand Slam quarter-final since 2010.That hoisted her seven places in the rankings up to just outside the top 10 at 11th.Surprise Melbourne semi-finalist Madison Keys gained 15 places to break into the top 20 for the first time in her career.