Hibs moved up to second in the Scottish Premier League with a dramatic late win at McDiarmid Park.
With the game heading for stalemate, Ben Williams saved Nigel Hasselbaink's penalty and Liam Craig's follow-up.
And Paul Cairney made Saints pay for the miss, firing low under goalkeeper Alan Mannus, with home captain Dave Mackay sent off in injury time.
Craig earlier hit the bar with a rasping free-kick on a frustrating night for hosts.
On a bitterly cold evening in the Fair City, both sides started the match in a cautious fashion and it was no surprise that the first chance came from a set-piece.
Hibs enjoyed a spell of pressure and carved out an opportunity when Leigh Griffiths teed up Eoin Doyle in a central position at the edge of the box, but the Irishman blazed narrowly over.
As the first half wore on, it appeared that the players' creativity had been frozen solid as the ball was given hefty thwacks up and down the field.
Gregory Tade was looking lively for Saints, however, and he was upended by Ryan McGivern at the edge of the box; Mackay taking the resultant free-kick which was deflected over.
The home side were on top as the first half drew to a close and, after Tade won another free-kick 25 yards from goal, Craig hammered the ball off the crossbar, via slight deflection.
Saints started the second half brightly with Tade picking up on a misjudged McGivern header, but his shot from a tight angle flew over the bar.
However, this sparked Hibs into life and they went on to enjoy their best spell of the match, forcing a succession of set-pieces and pushing play deep into the Saints half.
Griffiths whipped a free-kick into the Saints box, but it was whipped in so fast it evaded the head of the diving David Wotherspoon and went into the arms of the grateful Alan Mannus.
Paul Hanlon then met a Griffiths free-kick at the back post, but his header was deflected over the bar for a corner.
After weathering the Hibs pressure, Steven McLean and Rowan Vine both passed up great chances to break the deadlock, shooting tamely at Williams when set up inside the box.
Saints were then given a glorious opportunity to go ahead when Wotherspoon clipped the heels of Mackay inside the box and referee Craig Thomson pointed to the spot.
But Williams dived to his right to parry Hasselbaink's spot-kick and recovered brilliantly to deny Craig.
Manager Steve Lomas, angered by Hasselbaink taking the ball from regular penalty-taker Craig and missing, was shown a red card after his frustration boiled over.
It soon got worse for Lomas's side when Cairney latched on to a loose ball in the penalty area and coolly slotted the ball under Mannus.
The game ended with further sour notes for the home side when captain Mackay was shown a straight red card for an off-the-ball incident in injury time, shortly after substitute David Robertson was stretchered off with a suspected broken leg.