The Argentina striker raced in to score after Granada keeper Tono could only parry a Cesc Fabregas shot in the 50th minute.
Messi, Barca's all-time leading scorer, notched his 36th of the league campaign and has scored 300 goals in 365 official matches for the club.
The former youth-team player has now netted in a record 14 consecutive league matches, helping the La Liga leaders to pull 12 points clear of second-placed Atletico Madrid before Saturday's encounter.
