The former Springbok became the biggest name in Welsh rugby after arriving at Rodney Parade from Western Stormers in a blaze of publicity last autumn.
And he went some way to refunding Newport's investment by single-handedly kicking his club to a Â£80,000 pay-day next month.
That is how much the Black and Ambers are guaranteed following Montgomery's NINE penalties that sealed an exciting 27-23 semi-final victory over Bridgend at the Millennium Stadium.
"Percy's kicking was just mechanical," said team-mate Shane Howarth.
"We didn't really play that much better than Bridgend but we got into good positions and Percy just couldn't miss, he was phenomenal."
Bridgend outscored their opponents two tries to nil thanks to scores from Craig Warlow and Gareth Thomas either side of half-time.
But it was not enough to stop Newport reaching their second final in three years as the Montgomery-show continued without interruption.
Montgomery said: "We always knew a semi-final was going to be a tight game so any points were going to be crucial.
"We made a lot of mistakes, especially in the first half, but the boys showed a lot of passion and character and thankfully my kicking was on target.
"Kicking nine penalties out of nine in a semi-final will go down among my favourite memories."
In the May 3 final Newport will face the undoubted cup king of Welsh rugby, Llanelli, who steamrollered Cardiff 44-10 in the second of the back-to-back semi-finals.
Cardiff feared before the game that they may feel the back-lash of Llanelli's heartbreaking exit from the Heineken Cup to Perpignan the previous week.
And so it proved that they every reason to be concerned as Llanelli, 11-times winners of the Welsh cup, systematically tore the Blue and Blacks apart.
Llanelli coach Gareth Jenkins said: "Some people questioned whether our state of mind would be up for this match after being so depressed after the Perpignan game, but I think we proved it was."
Barry Davies, Stephen Jones, Garan Evans and Mark Jones all went as Llanelli killed off Cardiff's brief challenge, racing into a 27-5 half-time lead.
Pieter Muller had touched down for Dai Young's side but it proved a brief interruption to Llanelli's flurry as centres Leigh Davies and Matthew Watkins both went over in the second-half despite Scott Quinnell's yellow card for a professional foul. Rhys Williams grabbed a late run-away try for Cardiff.
PRINCIPALITY CUP SEMI-FINALS
NEWPORT 27 BRIDGEND 23
LLANELLI 44 CARDIFF 10