Lifting themselves from the sixth spot, the inaugural champions leap-frogged to the second place, while KKR, with 7 wins and 6 losses, only have a mathematical possibility of making the final-four.
Man-of the-match Watson it was, who made things possible for RR as he muscled his way to a brilliant 104 not out in 59 balls, consisting of 5 sixes and 9 fours, to help the side amass 199 for six at the Brabourne Stadium.
KKR suffered their second consecutive loss in three days to end with 15 points and their chances of moving ahead depends on other teams.
Unless the results of the last two matches of the league phase tomorrow pan in their favour, they will be out of the tournament.
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The day though belonged to Watson, who smashed five sixes and struck nine fours in his 59 ball blitz - the fourth hundred of this season - besides putting on a rollicking opening stand of 80 with Ajinkya Rahane (37).
Andre Russell was Knight Riders' most impressive bowler on view as he put the brakes first and then picked up 3 for 32. The most expensive was Azhar Mehmood (0-41 in 3 overs), a surprise inclusion for this do-or-die game after not figuring in a single game earlier.
The Steve Smith-side got off to a real flyer after opting to bat first by racing to their fifty in just five overs with openers Rahane and Watson in punishing mood.