The pyrotechnics promised by England's explosive batting line-up did not materialise in the rematch of the 2019 final and their 282-9 was, at best, competitive on a decent track at the Narendra Modi Stadium.
The bowlers fared little better as New Zealand romped home in 36.2 overs with Devon Conway and Rachin Ravindra smashing rapid hundreds.
Buttler accepted that England had been "completely outplayed" but the disappointment would not blur his perspective going forward in the tournament.
"The first thing that springs to mind is whether you lose by a run or a defeat like that, it is one loss at the start of a very long tournament," he told reporters.
"That’s something that I’d be encouraging everyone to remember.
"It's certainly a tough loss to take...but just as we, had we won the game, don't get too high, we don't get too low when we lose as well."
Joe Root top-scored for England with 77, while Buttler (43) and Jonny Bairstow (33) also made starts.
"We were probably looking at a score of 320-330 which would have allowed us to build some kind of pressure," said Buttler.
"But I thought the margin for error was very small on that wicket and two (New Zealand) batters played exceptional innings."
England rested Ben Stokes, who is nursing a minor hip injury, and tried Harry Brook, who made a brisk 25 at number four before his soft dismissal.
Buttler said it was not the first time England had suffered a heavy defeat.
"We're not robots. Sometimes you don't play as well as you would like. Everyone's working hard everyone's prepared well and as I said we were just a bit off," he said.
"There's plenty of stuff for us to work on and get better at the start of a long tournament."
England play Bangladesh in Dharamsala on Tuesday hoping to boost their net run-rate.
