Cartagines recorded a controversial come-from-behind 3-1 win over Herediano in the first leg of the Costa Rica Primera Division final.
Carlos Johnson, Mauricio Castillo and Randall Brenes were on the scoresheet after Victor Nunez had given the visitors the lead at Estadio Jose Rafael Fello Meza on Sunday.
It puts Cartagines in prime position to claim their fourth league title and first since 1940 ahead of the second leg on Saturday.
But it was Herediano who made the better start, grabbing a 25th-minute lead when Nunez headed in.
Johnson scrambled in the leveller for the hosts eight minutes into the second half, and it was awarded despite there being a hint of offside.
The home fans were sent into raptures just two minutes later as Castillo struck, side-footing in a well-executed set-piece.
Brenes added a controversial third on 63 minutes – tapping in from close range – as Cartagines again scored from what appeared to be an offside position.