Mendys, as it came at 0-0 when we were in total control and meant we were chasing the game.
We were in complete control when Sterling was put through, and would have been 2-1 up, completely dominating Chelsea and they'd have had to start chasing the game.
If Sterling passes we win, If Mendy doesn't give the ball away, it's 0-0 and we're still not winning, nor really breaking Chelsea down.