Messi struck twice in quick succession during the first half to put Barca in charge at the Nou Camp and he completed the 45th treble of his career late on after Nabil El Zhar had pulled a goal back for Leganes.
The youngster went on to add praise for his teammate Lionel Messi and how he shares the dressing room with the Argentine superstar, "It's great to play with Messi, and for me, it is a pleasure to be able to share a dressing room with the type of players who have won everything".
And El Zhar made up for that miss 22 minutes from time, picking his spot in finding the bottom corner from 18 yards, with the aid of a slight deflection off Sergi Roberto, after being set up by Gabriel Pires.
After being picked out by Philippe Coutinho, Messi then doubled the score-line, holding off two defenders before finding the net with a trademark finish, which he nearly passed into the goal.
The 20-year-old has, however, proved his worth since recovering match sharpness and claims his unshakable belief has not been knocked by critics of his forced exit from Borussia Dortmund or his debut campaign in La Liga. It's not easy to do something that hasn't been done for such a long time.
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Chiesa later said on Twitter that the New York State Athletic Commission determined he would not be allowed to fight on Saturday. That bus also contained Ray Borg , who's fight has also been cancelled due to fragments of glass getting in to his eye.
Barcelona remain unbeaten in La Liga this season, which is a remarkable achievement after 31 games.
That would draw them level with the 38-game unbeaten streak posted by Real Sociedad between 1979 and 1980, a run which remains a league record until this day.
Barcelona had eased off and gave Leganes a glimmer of hope-until Messi intervened once again.
Barca thrashed Roma 4-1 in the Champions League on Wednesday night, so they will be in high spirits as they chase the first ever unbeaten 38-game season in Spain's top flight.