Goalkeeper Brendan Clarke was again the hero for Paul Osam's Under 21 side, saving three shoot-out penalties for the second week in succession to secure a place in the Under 21 league final.
Despite having dominated the first half the Saints found themselves a goal down midway through the second when some neat passing and a cool finish saw Drogheda cut through the Pats defence.
The Saints had some good chances to equalise with both Andy Harran and Daniel Corcoran going close. However, it was left back Anthony Costigan who came up with the leveler right at the death. His 35 yard shot catching the Drogheda goalkeeper in no-mans land.
Both sides had chances to win the game in extra-time with the best chance falling to Corcoran. His header finished just wide of the far post after some good work by Harran down the right.
The penalty shoot-out saw Jack Flynn, Corcoran and Costigan slot home from the spot while Clarke saved all three of the home side's efforts.
The Saints now play UCD in the final which takes place this Thursday, 15th November in Belfield at 7.45 p.m.
St. Pats U21: B. Clarke: B. Rooney; A. Costigan; D. Foran; D. Moore: K. Cornwall; B. Slattery; J. Flynn; J. Hayden: A. Harran; D. Corcoran.
Subs: D. Fagan; A. Crowther; C. O'Connor; A. el Fridah, R. Horgan.