But Connacht are in good form at the moment and they were not to be denied, edging their way back from a 16-3 half-time deficit before Jarvis' late show.
Eric Elwood's men are searching for a highest-ever RaboDirect PRO12 finish and made it three wins on the bounce with this success, gaining some revenge from their defeat at the Stadio Luigi Zaffanella in the reverse fixture.
Aironi meanwhile, who will not be part of the league next season, fell short of a first away success by the narrowest of margins as they faded in the second half.
It was Italian fly-half Orquera who gave Aironi the early lead as he fired over a drop goal just before the quarter hour.
Miah Nikora levelled the scores midway through the half but Connacht were not level for long as second row Geldenhuys made his entrance.
The South African-born lock went over for his first RaboDirect PRO12 try on 23 minutes, Orquera's conversion making it 10-3.
The fly-half was on target again three minutes later and he stretched the lead to 13 with four minutes remaining in the half to make it 16-3 at the break.
Elwood reacted with three substitutions early in the second half with Adrian Flavin, Jonny O'Connor and Rodney Ah You all entering the fray.
And they edged back into the game when Nikora knocked over his second penalty on the hour mark.
Connacht continued to work their way back into it with Nikora slotting a third penalty of the day at the Sportsground to move the home side back to within a converted try.
With five minutes remaining Connacht were handed a boost when replacement Aironi second row Josh Furno was sin-binned.
And they capitalised immediately with Ah You going over, Nikora slotting the conversion to draw the home side level.
Having seen the Irish side claw their way back into it, Aironi then had to watch on in horror as replacement Jarvis found the target with a penalty in the final seconds of the game.
