After 10 dot balls, Watson opened his account but the story was entirely different after 47 deliveries.
The spectacular flourish that became his trademark has been replaced by tentative jabs at the ball, or fatal pre-determined shots.
Put into bat, Sunrisers struggled for momentum despite another important contribution from Williamson, who was stumped by opposite number MS Dhoni off the bowling of spinner Karn Sharma.
Soon the duo helped their team get past the 100-run mark in the 12th over and just after that Watson, who was looking at his best, hammered Sandeep to 27 runs in his final over.
Chennai, playing in its seventh final in the popular Twenty20 tournament, had previously won back-to-back titles in 2010 and 2011.
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He was supported by Yusuf Pathan who hit an unbeaten 45 off 25 balls, including four fours and two sixes.
The Australian along with Suresh Raina (32) forged a 117-run match-winning partnership to put Chennai ahead of their opponents. "It was outstanding, they didn't give us opportunities, they hit it over the fence rather than to our man. Look, it is such a fine line, I know out there on the park it's an eight-wicket win but we all saw that there were moments of pressure where the game can change very quickly, and if you're able to pounce on those then that's when you take your opportunity".
Watson completed his second IPL century of the season off 51 balls with a single at cover off Rashid's last over before smashing the Afghanistan legspinner for two consecutive boundaries. But it turned out to be a one-sided affair after that as Watson alone hammered 117 runs off just 57 balls as CSK cantered home in the 19th over with eight wickets to spare.
Watson was just one of nine members of the Chennai squad to be aged over 30.
"It is the fitness that really matters more than the age aspect", said the former India captain, 36.
"What captains want is players who move well in the field".
But Dhoni acknowledged that he could not push his whole team to run like a 20-year-old. You get given a role, and you try to adapt it the best you can.