Messi, who was included from the start, repaid fans who sat through a 30-minute delay due to weather conditions with a splendid performance.
Messi scored in the 11th and the 44th minutes. He has 14 goals in 12 Leagues Cup matches, one ahead of Los Angeles FC’s Denis Bouanga for most in the tournament’s four-year history.
After being held off the scoresheet against Columbus, it didn’t take Messi long to make an impact on Wednesday.
He fired a long cross from Allen past Andres Sanchez to equalise after David Rodriguez put San Luis ahead with a header four minutes into the match.
Messi finished from close range later in the first half and assisted on Micael’s header in stoppage time.
Luis Suarez was unavailable due to a suspension that will see him miss the entire tournament, but with Messi in this type of form, Inter Miami will believe they have all it takes to go all the way.