O'Gara scored six penalties from seven attempts in his first appearance for the province since Ireland's World Cup quarter-final exit at the hands of Wales.
It was a very different tale for Italy pivot Luciano Orquera who could not find his range from the kicking tee, missing three chances as Aironi struggled to spark in attack.
As a result the Italian side remain rooted to the bottom of the table with just one win to their name, a 25-19 success against Edinburgh in September, while Munster closed the gap on the Ospreys at the top of the table.
Munster took the lead after just four minutes as O'Gara slotting a penalty and the veteran fly-half was on target again soon after as he punished more Italian indiscipline to make it 6-0.
Orquera then missed his first shot at goal of the night but he soon made amends to bring the score back to 6-3.
The Azzurri fly-half was off-target again midway through the half, and after seeing Joshua Furno replaced by Italian international Quintin Geldenhuys five minutes from the end of the half, O'Gara notched up his third penalty.
There was still time for Aironi to earn another penalty but Orquera's radar was off again as his kick drifted wide.
O'Gara began the second half in the same way he ended the first, knocking over two penalties in the 43rd and 48th minutes to stretch the home side's lead to 15-3.
And having missed the target for the first time of the night five minutes later, the 34-year-old found his range again soon after to put Munster 15 points clear.
Despite the loss of prop Fabio Staibano to the sin bin, Aironi did manage to come back into the game as Orquera found the target with 15 minutes to go but it wasn't enough.
|Munster Rugby Score Card|
|Aironi Rugby Score Card|