Pontypridd recorded a magnificent victory at Vicarage Road as they became the first Welsh side to reach the semi-finals of the PARKER PEN SHIELD.
A try in each half for the Welshmen put paid to the English premiership side and made them only the sixth team in 24 quarter-finals to win away from home.
While there was plenty of attacking intent from the visitors in the first half, they had to rely on the woodwork at the death to deny the Saracens as former Springbok outside-half Jannie De Beer struck an upright with a 45-metre penalty that would have won the game.
More than that, Ponty then had to suffer a scrum under their own posts after a knock-on when the ball rebounded back from the penalty.
Saracens went for the drop goal, but Ponty somehow managed to force De Beer, the man who once drop-kicked England out of the Rugby World Cup finals in Paris with five drop goals, onto his left foot.
De Beer's kick drifted wide and the game ended as soon as the ball went dead.
Ponty were good value for their victory as they scored a try in each half to make it a notable day for Welsh rugby with Llanelli also beating Bath in the Heineken Cup.
No 8 Michael Owen was credited with the first try a minute before half-time that gave the visitors a 10-6 interval lead once Brett Davey had added the conversion.
De Beer struck three successive penalties in the first 10 minutes of the second half to hoist Saracens into a 15-10 lead, but Gareth Wyatt skipped away for the vital score five minutes later and Davey once again added a conversion.
After that, it was all about brave and organised defence and Ponty came up trumps - with a little bit of help from the upright.
SCORERS: Saracens: Pens: J de Beer 5. Pontypridd: Tries: M Owen, G Wyatt; Cons: B Davey 2; Pen: B Davey .
Saracens: T Horan; G Arasa, T Shanklin, K Sorrell (A Winnan 47), D O'Mahoney; J de Beer, K Bracken (captain, N Walshe 55); D Flatman (M Cairns 70), R Russell, P Du Randt, S Hooper (K Roche 47), S Murray, K Chesney, T Roques, R Hill.
Pontypridd: B Davey; G Wyatt, S Parker, J Bryant, N Simpason; C Sweeney, P John (captain); G Jenkins, M Davies, D Bell, B Cockbain (G Remnant 50), R Sidoli, N Kelly (D McIntosh 46), R Parks, M Owen.
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