England defeated New Zealand by 20 runs in their Super 12 contest after Buttler led by example and smashed 73 runs, while Alex Hales (33) hit a half-century.
New Zealand, England and Australia are tied on five points and occupy the first, second and third spots respectively in Group 1, separated by the net run rate. They all have one game left to play.
"I think it's a big relief to be heading to that last game knowing we have a chance at progressing," Buttler told reporters.
"So, yeah, we go there really excited. I think the team is in a really good place after tonight. Again, as I said earlier, it showed great character in a must-win match.
"We'll head to Sydney full of confidence and expecting a really tough game against Sri Lanka."
New Zealand face Ireland and Australia play Afghanistan in their final group game on Friday. With England set to play Sri Lanka the next day, Buttler's team will know exactly what they require to qualify.
"There is a little bit of a benefit obviously playing that last game to know exactly what is required of us," Buttler said.
SANTNER PRAISES ENGLAND'S DEATH BOWLING
New Zealand all-rounder Mitchell Santner (30), who finished with an unbeaten 16 but failed to take his side home, said they were in with a chance with Glenn Phillips (25) still at the crease but were undone by some fine bowling at the death from England.
"If you look at the position we kind of got ourselves in was a good one. I guess the run rate might have been at 12s, but we still had a few wickets in the tank," he said.
"But I think credit goes to the way England bowled there at the end. Woakesy (Chris Woakes) and Sam Curran made it tough to score, and if you can chip wickets out at the end, it kind of dents the momentum."
Santner said New Zealand would not take Ireland lightly given their surprise win over England earlier in the competition.
"I guess the nature of T20 cricket, if one or two guys step up on the day, they can kind of turn games... we'll do our prep and see what we're going to get against and format a plan against a pretty good side."
