The brief 30-second-long clip sees preparations build for the MCU heroes’ almighty battle with Thanos.
Iron Man (Robert Downey Jr) takes centre stage as he says ominously: “So this is it.
“It’s all been leading to this!”
Also seen are Tom Holland (Spider-Man), Chris Hemsworth (Thor) and Chris Evans (Captain America).
Karen Gillan also gets her own close-up as Nebula, along with Scarlett Johansson (Black Widow) and Benedict Cumberbatch (Doctor Strange).
The teaser is the first proper footage fans will have seen since the record-breaking full trailer was unveiled late last year.
In just four hours it has accrued 35,000 Likes and 22,000 Retweets on Twitter, with 4.1 million spins on Facebook already accounted for.
“EVERYONE GO HOME MARVEL WON THE SUPER BOWL,” read one reply on Twitter.
“I am SO there for this!!!!!!!!!!!!!!!!!!!” said someone else enthusiastically.
Infinity War will lead directly on to the as-yet-untitled Avengers 4, released next year. Both movies have now wrapped filming.
Avengers: Infinity War is out on April 27 in the UK.