Watson smashed an unbeaten 90 as Rajasthan made 126 for three in only 16.2 overs after Tait had taken three for 13 to help restrict the home side to a meager 125 for six at Subrata Roy Sahara Stadium.
Watson hammered four sixes and 10 fours from 51 balls against the hapless Sourav Ganguly-led side.
Watson, who came in to bat at No 3, belted left-arm spinner Murali Kartik for 16 in an over and took 15 off five deliveries from pace bowler Ashish Nehra.
The all-rounder's dominance was demonstrated by the next highest scorer for his team being Ashok Menaria with 18. "The wicket was a bit slow, I suppose it was my night tonight," Watson said. "I just back myself. I have a clear mind and try to hit straight."
Earlier, Tait struck at timely intervals to stop Pune getting a partnership going.
Ganguly was Tait's first dismissal, the batsman miscuing an attempted pull off a well-directed bouncer to be out for 14. Robin Uthappa (13) and Mithun Manhas (11) were his other wickets, the bowler varying the length of his deliveries and his pace often having the batsmen hopping about.
Anustup Majumdar, who played for Kolkata Knight Riders before moving to Pune last year, was the top-scorer for his team with 30 from 20 balls, hitting two sixes and a four.
The win lifted Rajasthan, the 2008 champions, into fourth place in the nine-team league with six wins and six losses from 12 games. Pune are next-to-last with four wins and nine losses from 13 games and virtually out of contention for the play-offs.
Punjab moved up to fifth position with every reason to hope for a play-off finish.
Mandeep, who opened the innings for Punjab after being put in to bat by hosts Deccan Chargers, stroked a fluent fifty off just 48 deliveries laced with three sixes and eight boundaries.
It was a knock that inspired David Hussey, Mandeep’s captain, to predict an India cap for the 20-year-old batsman.
“Mandeep is going from strength to strength. I think he’s a future players in all three forms [of the game] for India,” said Hussey, leading the side in place of the injured Adam Gilchrist, at the port-match presentation ceremony.
Mandeep also received able support from Shaun Marsh (22) before Kings XI reached 170 for eight thanks to a quickfire 28 not out from David Miller.
It was a scoreline that proved too high for the Chargers as, once again, none of their batsmen built on their promising starts.
Daniel Harris top-scored with 30 and none of the other players even reached 20. Hussey (2-2), Praveen Kumar (2-15) and the in-form Parvinder Awana (2-27) all came to the Punjab party.
Kumar Sangakkara, the losing captain, admitted the visitors could have been limited to a smaller total.
“I thought the difference today was the bowling in the first four overs. We bowled too short on a wicket that still had something in it for the bowlers. Kings XI showed us how to bowl and where to bowl.”
Follow us @SprtNationalUAE