After Willian had given the hosts the lead, Barca knew that they needed to find some way of ensuring that they did not go into the return leg in a losing position and in the end they were handed a way back into the game.
Andreas Christensen played a poorly-judged pass across his own defence and Andres Iniesta was on it as quick as a flash.
The Spaniard jinked past fellow counteryman Cesar Azpilicueta before driving forward and squaring for Messi to sweep home from just inside the box to draw the game level.
It was Messi's first goal in nine games against Chelsea and came with his 30th shot against the 'Blues'.
Check out the strike for yourself below:
20 February 2018