After restricting India to 229, England were bowled out inside the 35th over to suffer a fifth defeat in six games.
Only an unlikely mathematical miracle will save England who are rock-bottom of the 10-nation tournament having won fewer games than even non-Test playing Netherlands.
"Very disappointing. At the halfway stage chasing 230 we fancied ourselves. But it's the same old story," said Buttler.
"The gut feeling was that we wanted to chase. It is as good as we have been with the ball throughout the tournament. We took some good wickets so we are very disappointed."
The weary-looking skipper added: "Whatever way you want to approach the game it is about being committed. For me it was soaking up pressure, building up partnerships and killing pressure.
"It is a about executing your skills. Chasing 230 there wasn't scoreboard pressure, we are falling short."
India skipper Rohit Sharma led the charge for his team with 87 as India posted 229-9, a total that looked below par but proved enough for a struggling England side on a sluggish pitch.
Fast bowler Mohammed Shami returned figures of 4-22 while fellow quick Jasprit Bumrah took three wickets to wrap up the match.
England had a disastrous start and never recovered from being 52-5.
"This was a game that showed a lot of character in our squad. When times were tough, our experienced players stood up at the right time and fought for us," said Rohit, his country's top run scorer in the tournament after Virat Kohli was out for nought.
"Defending 230 is not something you see every day. You know you have got to take early wickets and put the pressure on. With the experience that our seamers have, I can always rely on them to come good."
Rohit added: "We have got a good balance in our attack. Good spinners and experienced seamers. If I look at my options as a captain, there is plenty for me to work with.
"It is also important that our batsmen put scores on the board so that they can work their magic."
