Sehwag was unbeaten on a 131-ball 103 and Sourav Ganguly was on nine at lunch
Tourists lead by 105 runs with eight wickets in hand and two sessions to go meant Test is heading towards a draw.
Resuming at the overnight score of 45/1, India added 97 off 24 overs in the first session before losing the wicket of Tendulkar while Dravid was retd hurt.
Sehwag surviving the early scares settled into groove to keep the score mounting even as his partners Dravid and Tendulkar were mere onlookers during their stand of 71 off 84 balls.
Dravid faced 21 balls without adding to his overnight score, then retired hurt with a damaged right middle finger. He was struck by a lifter from Lee and reluctantly left to the dressing room.
The extent of the damage was not known but an Indian team spokesman said Dravid was having x-rays.
Sehwag was not afraid to swing left-arm spinner Brad Hogg over wide mid-wicket for six - one of two sixes for the innings - and he also hit nine fours.
He raised his hundred with an on-side push for one off Johnson, and leapt and punched the air jubilantly as he passed the stumps - and then hugged Tendulkar.
This was his 13th century in 54 Tests, including his third in 12 Tests against Australia. The 29-year-old from Delhi made 195 in Melbourne and 155 in Chennai (formerly Madras) - both in 2003-04.
Sachin Tendulkar (13) was run out nearing lunch. He took off for a quick single after pushing a ball from Mitchell Johnson to the off-side, but Johnson swooped on it and threw down the stumps while Tendulkar tried in vain to regain his ground.
Playing probably his final Test innings in Australia, Tendulkar received his now-mandatory standing ovation before and after his dismissal.
Brief Scores (at lunch, D-5):
India 526 and 142/2 (Sehwag 103, Dravid 11 retd hurt; Johnson 1 for 15) Vs Australia 563.