In rain-soaked conditions, Keatley kicked a penalty and scored a late try for an 8-0 interval lead. The Connacht out-half added a second penalty, but Tito Tebaldi's penalty double saw Aironi snatched a deserved bonus point.
Overall, Connacht did enough to collect their fifth straight home win for their best run of form in Galway since the 2005/06 season.
In the opening minutes the Italians kept Connacht out after two smashing touchfinders from Keatley, who missed a subsequent 30-metre penalty.
A bout of aimless kicking was ended by a Ray Ofisa-inspired breakout which resulted in Connacht's forwards storming through and Keatley landed the first points.
The visitors were doing well to frustrate Connacht, and Joshua Furno, Gareth Krause and Nick Williams were heavily involved up front.
Both try-lines remained untroubled during a listless spell, with James Marshall and Kaine Robertson covering Keatley's kicks and Aironi's maul well-defended by Connacht.
A scrum infringement called against Aironi prop Ulises Gamboa allowed Keatley a third shot at the posts, but his 40-metre effort went narrowly wide.
Fionn Carr also had a try ruled out for a forward pass from Keatley and Connacht lacked penetration until first half injury-time.
A neat wraparound move involving Keatley and Troy Nathan sent the out-half hurtling towards the Aironi line and although Riccardo Bocchino made the tackle, Keatley's momentum took him over.
Television match official Jude Quinn confirmed the score and Keatley's missed conversion left eight points between the sides at half-time.
Connacht looked poised to add to their tally from a close range scrum, early in the second half, but Aironi snaffled turnover ball and cleared the danger.
Carr's pace was causing more problems for Aironi, and Keatley converted the second of two penalty attempts to make it 11-0.
Eric Elwood's men just could not cut loose though, and the arrival of snow hampered their attacks. Aironi kept plugging away, marshalled by a determined Marco Bortolami.
Replacement winger Giulio Toniolatti was held up just short of the Connacht whitewash, with the ever-alert Frank Murphy coming to his side's rescue.
Play was brought back for a penalty which Tebaldi knocked over. A powerful run from Williams got Rowland Phillips' side back on the front foot and Tebaldi's 75th-minute penalty was the final scoring act.
|Connacht Rugby Score Card|
|Aironi Rugby Score Card|