The 23-year-old scored his second goal in as many games with five minutes remaining, helping the Toffees record their first win at Old Trafford since the 1992-1993 season.
"I'm very happy with the winner because we haven't won at Old Trafford in 21 years," talkSPORT quotes the Costa Rica international as saying.
"Yesterday the manager (Roberto Martinez) said in the meeting that today is a final for us and it was a final for us. We needed to work and play hard in the game because it was very important for us.
"We're working to qualify for the Champions League. That's very important for me and the team because that's my dream to play in the Champions League with Everton."
The Blues are fifth in the table, level on points with Merseyside rivals Liverpool.