Youth international Locadia, whose treble gave PSV a 3-0 win over Zwolle, got his chance after Jeremain Lens was suspended for three matches after a clash on and off the pitch with Feyenoord's Joris Mathijsen in a league match on Sunday.
The 19-year-old opened his account with a simple finish on 16 minutes after being set up by Georginio Wijnaldum.
"It looked easy today because we kept focused but because we did not finish it earlier Zwolle kept believing in it," said PSV coach Dick Advocaat.
"Reaching the final is a good finish after some turbulent days and I have to say that my players reacted well today," he added referring to the Feyenoord defeat and the altercation between Lens and Mathijsen.
All the goals came in the final 16 minutes, sparked by Jozy Altidore's goal from close range.
"This is great feeling and hopefully this match will give us confidence for the remaining 10 league matches," said Altidore.
