Serena and Venus Williams are on track for a sisters semifinal at the Australian Open after fourth round wins. Venus advanced to the quarterfinals for the seventh time by beating Italy's Francesca Schiavone 3-6, 6-2, 6-1 in the opening match. Defending champion Serena had a 6-4, 6-2 win over Australia's Sam Stosur.In men's fourth-round matches, Novak Djokovic beat Poland's Lukasz Kubot 6-1, 6-2, 7-5 to set up a quarterfinal against Jo-Wilfried Tsonga.