Ernesto Valverde's side moved 12 points clear at the top of the table, extended their unbeaten league run this season to 31 matches and equalled a LaLiga record of 38 games unbeaten - set by Real Sociedad between 1979 and 1980. The versatile 26-year-old has been used predominantly at right-back this season, although he featured in midfield against Roma in the UEFA Champions League on Wednesday.
After the interval, Barcelona's measured close to the first half seemed to carry over into the second, with Valverde's men offering little urgency in possession and remaining content to maintain a controlled tempo.
"We will see [on Saturday]", Valverde said in a news conference when asked if Messi would start against Leganes. Not many full-backs would look forward to facing that double threat.
Messi clearly proved his fitness to Valverde and then went on to show he is still in peak form.
Barcelona will have the chance to own that record outright next time out when they welcome Valencia to Camp Nou on Saturday. And this was yet another display of the Argentinean's brilliance, with Barcelona once again dependent on their number 10.
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There is some pressure on Barcelona to end the season unbeaten, something that the Blaugrana have never managed before, but El Txinguirri has denied this. "And when he's scoring goals that always helps".
The Leganes game is the third of seven matches in a 22 day period for Barca, with the Champions League quarterfinal second leg against Roma and the Copa del Rey final against Sevilla to come before April 21.
Leganes ought to have scored straight after the break when Claudio Beauvue headed narrowly over the goal after replacing Nordin Amrabat.
Leganes nearly threw a spanner in the works early in the second half when El Zhar's cross from the right met by Claudio Beauvue's powerful header, which only just cleared Marc-Andre ter Stegen's crossbar.
Five minutes later, the Argentine bagged his and Barca's second on the night with a clinical finish after being played in by Philippe Coutinho.