England not doing themselves justice - Buttler
England followed the trend of a bowler-dominated series, losing early wickets after being put into bat by Rohit Sharma in the decider on Sunday.
But new white-ball captain Buttler led the recovery with 60 alongside Moeen Ali (34) before Craig Overton's 32 helped the hosts post 259 all out.
England appeared well-placed to defend the total when Reece Topley dismissed Shikhar Dhawan, Rohit and Virat Kohli to leave India reeling at 38-3.
Yet Rishabh Pant combined with Hardik Pandya (71) for an unbroken stand of 133 as the wicketkeeper-batsman crafted his maiden ODI century, guiding the tourists to a five-wicket victory with 47 balls to spare.
Pant dazzled with his 125 off 113 deliveries, but Buttler missed a glorious stumping chance when the left-hander was on just 18 and paid a heavy price.
"It was a good wicket once you got yourself in, so we were a bit light with the bat. But the start we made with the ball gave us a chance and that missed stumping cost us," Buttler said.
"Pant is a really good player. If you give good players a chance they will hurt you and had we taken those chances we had a good hold with a long tail. But with the score we put up we had to take all our chances.
"We are not quite hitting our straps as a batting unit, but we are not far off. We are just not producing what we are capable of. So hopefully individually and collectively we can find a solution.
"These guys are fantastic to work and there is still a lot of enjoyment. Hopefully we will find our best cricket soon.
"I am an experienced cricketer but a young captain, so I am not worrying too much. I have lots to learn, and I need time to do that."
Hardik set the tone with the ball for India with career-best ODI figures of 4-24 that included the all-rounder having the final say in a short-ball battle with Liam Livingstone (27) by getting him caught on the boundary.
Livingstone and Hardik exchanged words throughout the contest and, despite the India star's wry smile upon the England batter's dismissal, he says the pair's relationship is amicable.
"White ball cricket is something very close to me," Hardik said after India completed 2-1 series victories over England in both the T20I and ODIs.
"I cherish my white-ball game. We all know England are such a good team. For us it was important to check ourselves out with our plans and the World Cup ahead.
"It was an ideal chance for us to step up and show what we have. It was important for me to come in and stop the runs and bowl as many dots.
"We took two wickets early, but they recovered well and were cruising. I love short balls. I don't fancy people taking me on, it always gets me into the game.
"I don't mind getting hit for six sixes as long as I take wickets. I am good pals [with Livingstone] but at the end of the day that's his game. He takes his chances on."
Hardik was also quick to hail the efforts of Pant, saying: "Today he played the situation. Our partnership changed the game and the way he finished the game was special."