Barca struggled to settle in the opening spell as Leganés pressed, harried and pressured, but with their first chance they opened the scoring, when Luis Suárez beat his man on a sprint down the right and set up Lionel Messi for a tap in.
Two more clinical moves in the first half saw the MSN all the scoresheet by half-time, the first time that's happened in a Liga match. Messi set up Suárez for the second, and Suárez then turned provider for Neymar just before the break.
Leganés to their credit never gave up and despite losing another two goals - including a Rafinha screamer. They kept going forward until they got a consolation goal, a superb free-kick from Gabriel.