"I feel pretty good," Smith said. "Everything's working for me at the moment, which is nice."
India worked hard in reply and reached 108 for 1 at stumps in reply to Australia's first-innings total.
Murali Vijay brought up his fourth half century of the series and Cheteshwar Pujara was unbeaten on 25 at the end of play.
The Indian batsmen made a watchful start to their chase, content to leave the ball rather than risk a wicket before stumps.
Pujara got a lucky escape while on 12 when an edge carried to Brad Haddin, who fumbled the catch.
Smith was earlier ably assisted by Brad Haddin (55) and fast bowler Harris (74), to help the Australians add 271 runs to their overnight score.
Smith was the last Australian out, bowled middle stump playing at an Umesh Yadav (3-130) ball. His knock came off 305 balls with 15 boundaries and two sixes.
Harris scored his third test half century in style with eight fours and a six before he was trapped lbw while attempting a big sweep off Ravichandran Ashwin (3-134).
Smith and Haddin turned an evenly-poised match in Australia's favour with an aggressive start to the morning, sharing a 110-run, sixth-wicket partnership until Haddin offered a bottom edge to India wicketkeeper MS Dhoni off Mohammed Shami.
Smith added another 50 runs with Mitchell Johnson, who scored 28 before being stumped off Ravichandran Ashwin before lunch.
Smith's previous highest first-class score was 177 scored for New South Wales against Tasmania. Australia can clinch the four-test series with a win or draw in Melbourne after a 48-run win in the first test and a four-wicket victory last week in the second test at Brisbane.
-Agencies