A gritty century from Kaushal Silva gave Sri Lanka a commanding 288-run second innings lead today, dimming Australia's hopes of a consolation win in the third and final Test in Colombo.Sri Lanka, who are pushing for a rare series whitewashafter winning the first two Tests, were 312 for eight at stumps on the fourth day.First innings centurion Dhananjaya de Silva was unbeaten on 44 with Suranga Lakmal yet to get off the mark at close of play.Silva made a composed 115. He put together a crucial 90-run partnership with first innings centurion Dinesh Chandimal.Sri Lanka, who resumed Tuesday on 22 for one, quickly scored two runs to erase the 24-run first innings deficit.Earlier, veteran spinner Rangana Herath led the Sri Lankan attack, snaring six wickets, with Australia all out for 379 in response to Sri Lanka's 355.