Messi scored his ninth goal in just his sixth game for the MLS team as they won 4-1 in the semi-final.
The Argentina maestro shrugged off an ankle injury, picked up in training, to start the match.
He netted a long range effort in the 20th minute, while Josef Martinez, Jordi Alba and David Ruiz were also on target for Miami.
It keeps up Messi's incredible record of scoring or assisting in every single game he has played in since joining David Beckham's franchise.
Across his whole career, there are just four teams that he has failed to do just that against.
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The 36-year-old has faced 119 different sides, scoring against 104 of them and scoring or assisting against 115.
The lucky four are Bordeaux, UDA Gramenet, Udinese, and Rubin Kazan.
Messi will be hoping to add a new name to that list on Sunday when Inter Miami face Nashville in the Leagues Cup final.
It will be the 42nd final of his career and also means Miami have qualified for the Concacaf Champions Cup regional tournament.
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That could also open up an opportunity to qualify for the expanded Club World Cup in 2025.
"Our goal was to qualify for international competition next season and we've done that," said Miami boss Gerardo Martino.
"Now we have to prepare to win this tournament, which has us feeling very motivated and confident."