The Argentinian took his goals tally to 60 for the season after coming on as a substitute with his side being held 2-2 by the spirited visitors and facing a real threat to their 13-month unbeaten home record in La Liga.
While the Catalan faithful revelled in Messi's display, his 35-minute cameo did little to dispel the growing - if unfair - theory that Barca are a one-man team.
Certainly the hosts looked shaky before his introduction, with Betis twice taking the lead through Dorlan Pabon and Ruben Perez.
Within minutes Messi curled home a wonderful free-kick to hand his side the lead for the first time and leave many in the Nou Camp shaking their heads in disbelief.
But Messi was not finished there and moments later was applying the finish to a sublime team move that secured the points and means Barcelona can be crowned champions before they next kick a ball in anger should nearest challengers Real Madrid fail to beat Malaga on Wednesday and Espanyol next Saturday.