The Aussie skipper became only the third batsman along with Don Bradman and Jacques Kallis to score tons in four consecutive Tests in the same series as his team posted a total beyond 500 for the fourth Test running.
Smith contributed 117 in Australia’s first innings declaration of 572 for seven before the tourists were rocked by the third-ball dismissal of opener Murali Vijay for a duck.
At the close, India had stabilised at 71 for one to trail Australia by 501 with Lokesh Rahul on 31 and Rohit Sharma hitting two sixes on his way to 40 not out.
Left-armer Mitchell Starc, bowling with fire and rhythm, slanted one across Vijay and coaxed a snick to wicketkeeper Brad Haddin.
Starc may get into disciplinary trouble for giving Vijay a big send-off, roaring in his face and waving his fists in a fiery opening over as Mitchell Johnson’s injury replacement.
But the day belonged to Smith, who added another century to his unbeaten 162 in Adelaide, 133 in Brisbane and 192 in Melbourne in this series.
Australia passed 500 for the fourth Test of the series, a feat last registered against the Garry Sobers-led West Indies at home in 1968-69.
Smith was out just before lunch when he was caught behind off Umesh Yadav ending his 208-ball knock spiced with 15 fours.
He has 698 runs in the series at an average of 139.6, placing him third behind Bradman (715) and Ricky Ponting (706) for most runs in a series against India.
Smith is having an extraordinary purple patch and has now scored six centuries in the first innings of his last seven Tests at home.
Watson again missed out on what would have been only his fifth Test century when, on a flat SCG wicket, he had another brain snap and hoisted Mohammed Shami straight to Ravichandran Ashwin at deep midwicket for 81.
Watson has now scored 24 half-centuries but just four tons in 56 Tests, with his last Test hundred coming against England in Perth in December 2013.
He toiled for 250 minutes and faced 183 balls in putting on 196 runs for the third wicket with Smith.
Shaun Marsh added 73 to his 99 in Melbourne before he was caught behind off Shami nearing tea. Marsh batted for 116 balls with nine fours and a six.
Joe Burns, playing in his second Test, was well caught by Rahul in the deep for 58 off 114 balls and Ryan Harris roused the crowd with a lusty 25 off nine balls before the declaration.
It was hard going on the unresponsive SCG pitch for India’s bowlers with Shami finishing with five for 112 off 28.3 overs.
India have already lost the Border-Gavaskar Trophy with Australia holding an unassailable 2-0 lead following wins in Adelaide and Brisbane.
The tourists have won only one of their last 22 Tests overseas and have been successful in only one of their 10 Tests at the Sydney Cricket Ground, that sole victory coming 37 years ago. (AFP)