India's Mahesh Bhupati and Rohan Boppana have qualified for the Men's Doubles Semi-finals of the ATP World Tour Finals at London. They beat Daniel Nester of Canada and Max Mirny, 7-6, 6-7,10-5. Meanwhile, defending champion Roger Federer guaranteed his place in the last four stage of the men's singles with a straight-sets win over Spain's David Ferrer today.The Swiss world number two, bidding for a record-extending seventh title at the end-of-season finale, beat Ferrer in a 6-4, 7-6 taking his career record over the tenacious Spaniard to 14-0. In another match Juan Del Petro of Argentina beat Janco Tipsarovic of Sarbia 6-0, 6-4.Earlier, Novak Djokovic squeezed past Britain's Andy Murray with a 4-6, 6-3, 7-5 victory but ended the day still uncertain of a place in the last four after Tomas Berdych overpowered Jo-Wilfried Tsonga. Victory for Tsonga later against Berdych would have guaranteed Djokovic a top-two finish in the group and progress to the semis but Berdych's 7-5, 3-6, 6-1 victory means all four players, even winless Tsonga, could still qualify for the semi-finals.