Benfica survived the first-half sending off of defender Sidnei to win a physical city derby against Sporting Lisbon 2-0 on Monday.The win illustrated the gulf in quality between the two Lisbon sides this Liga Sagres season, with second-placed Benfica now 15 points ahead of their bitter rivals in third.It took just 15 minutes for Benfica to take the lead. A cross from the right was only cleared by Sporting's defence into the path of Eduardo Salvio - one of five Argentine players on the pitch - who took one touch before firing past goalkeeper Rui Patricio from close range.Sporting quickly went about seeking an equaliser, with striker Yannick Djalo flashing a right-footed drive just wide and new Brazilian signing Cristiano finding the back of the net only for the goal to be ruled out for off-side.Their job was made easier when Benfica central defender Sidnei was dismissed for his second yellow card inside five minutes as the first half drew to a close.And Sporting almost restored parity in the 52nd minute when strike duo Helder Postiga and Djalo drew a double save out of Benfica shot-stopper Roberto Jimenez.Cristiano needed attention after coming off second best in an aerial challenge with Benfica striker Oscar Cardozo in the lead up to the double chance, highlighting the increasingly bruising tone of the match.Sporting - still struggling to adapt to life without regular top-scorer Liedson, who was sold back to Brazilian club Corinthians in January - had the majority of their chances to draw level from outside the area, with Djalo again firing wide from distance in the 59th minute.And their inability to find a way through their opponents' now-three man defence was punished when Nicolas Gaitan volleyed home from inside the box.Benfica had won a free kick on the edge of the area, with Sporting captain Anderson Polga perhaps fortunate not to join Sidnei in the dressing room after he brought down a theatrical Gaitan as the last man.The free kick was initially cleared, but Maxi Pereira's cross back into the area was volleyed first time by Gaitan, though Rui Patricio's efforts to save the shot were not helped by a wicked deflection.Substitutes Diogo Salomao and Maniche both tried to their luck for Sporting as time ran out, but bragging rights emphatically belonged to Benfica.Sporting must now attempt to hold on to third place on the Liga Sagres table, with Vitoria Guimares just one point in arrears.Benfica's win puts them 15 points above their Lisbon rivals, though they still trail league-leaders Porto by eight points.