Benfica beat Porto in semi-final first leg
Portugal left-back Coentrao took advantage of a mix-up between keeper Helton and centre back Maicon to toe-poke in the first in the sixth minute.
Spanish midfielder Garcia scored the Portuguese champions' second 20 minutes later from long-distance after a poor clearance by midfielder Fernando.
Porto, unbeaten in the Portuguese Premier League and eight points ahead of Benfica, were a shadow of the team that had thrashed their Lisbon rivals 5-0 on their last visit in November and failed to pose any consistent danger.
They missed their prolific Colombian striker Radamel Falcao, who was out injured, and could not break down a well-organised Benfica defence even after Coentrao was dismissed for a second booking on 59 minutes.
The second leg will be played in Lisbon on April 19.