Trailing 17-12 with two minutes left on the clock, Portora produced a fine move which resulted in Nathan Richmond touching down before James Stevenson slotted over the conversion to give them the victory.
The visitors Regent House started the stronger team, and after five minutes of pressure their winger went over in the corner.
The conversion attempt was missed leaving the home side trailing 5-0.
Portora replied strongly by turning over a ruck, and strong runs by Nathan Richmond and Peter Stubbs, took Portora to their opposition's 22 metre line.
Two penalty attempts were then missed by Portora scrum-half James Stevenson, kicking into a brisk wind, and his game got worse when he was sin-binned on the 25 minute mark by a strict referee after a dangerous tackle.
The versatile Nathan Richmond stepped in behind the scrum, as Portora soaked up relentless Regent pressure.
Having paid his penalty, Stevenson retook the pitch. He linked with Robert Connor from a scrum, and the Portora out-half broke the Regent line and sped in 25 metres for a magnificent try. Stevenson converted, leaving the half time score 7-5 to the home side.
Within five minutes of the restart, the Portora back line flashed the ball to the left and Ali Crawford, playing in the centre, broke the line and powered 30 metres across the line in the left hand corner. Stevenson saw his conversion effort drop just short.
Going 12-5 down seemed to waken the Regent House pack, and countless penalties followed, pinning Portora in their own 22. So intense was the battle between the opposing packs that at one point the referee found himself between them and was flattened to the ground.
Finally Regent linked the ball to the left hand corner and their winger made it over for their second try. This went unconverted leaving the score 12-10.
As Portora struggled to hold onto the game, two of their pack, Ollie Gamble and Nathan Aiken found themselves sin-binned by the strict referee.
The 13 man Portora team now came under permanent attack from a Regent team who could smell victory, and eventually they drove in under the posts, and saw this try converted. 12-17 down and two minutes to play.
Gamble returned with Aiken to muster his pack, but the Regent attack and Portora defence had come at a cost and young Jamie Gibson saw a fine display come to an end with a head injury. He was replaced at hooker by Stephen Roberts.
From the kick-off the Regent prop knocked on and handed the possession back to Portora.
In the final move of the match, Stevenson picked up at the base of the scrum, linked with Robert Connor who placed a beautiful grubber-kick straight through the Regent defence, and saw his effort chased down by Nathan Richmond in full flight, for the third Portora try.The move of the match.
With the score now at 17-17, and with no time left on the clock, Stevenson slotted the conversion to the sound of the referee blowing the final whistle. Portora 19-Regent House 17.
This had not been a game for the faint-hearted. Now, with three consecutive home victories behind them, the Portora 1st XV face a tough opposition from travelling side Armagh Royal next weekend.