The Ospreys had to rely on a late James Hook penalty to see off Aironi 12-10 in a nervy win that booked their spot in the Magners League play-offs.
Dan Biggar became only the second Ospreys player to reach 500 points in the Magners League as he kicked nine points, but four missed penalties by the fly-half almost cost his side.
Aironi had come within minutes of only their second victory in the Magners League. Danwel Demas scored the only try of the game for the Italians, while Tito Tebaldi kicked five-points.
The Ospreys headed into the game relying on the Scarlets to beat Cardiff, or a bonus-point victory for themselves. That never looked likely as the Aironi defence stayed strong throughout, but their ill-discipline gave Biggar plenty of opportunities.
After missing an effort in the opening minutes, Biggar made no mistake with his second on 18 minutes and brought up his personal milestone.
However, Aironi battled back and wing Demas scored the contests only try on the half-hour mark. Tebaldi's conversion gave the Italians a four-point advantage at the interval.
A penalty from Tebaldi increased the lead eight-minutes into the second half but Biggar hit back with two kicks of his own to leave the tie finely balanced at 10-9.
With news that the Scarlets were beating Cardiff coming through, Ospreys knew they only needed another score to take them into the play-offs and Hook stepped up to the plate.
Pen: Biggar 3, Hook
Aironi: 15 Horacio San Martin, 14 Matteo Pratichetti, 13 Gilberto Pavan, 12 Gabriel Pizarro, 11 Danwel Demas, 10 James Marshall, 9 Tito Tebaldi, 8 Gareth Krause, 7 Josh Sole, 6 Joshua Furno, 5 Quintin Geldenhuys (capt), 4 Marco Bortolami, 3 Fabio Staibano, 2 Luigi Ferraro, 1 Alberto De Marchi.
Replacements: 16 Fabio Ongaro, 17 Andrea De Marchi, 18 Luca Redolfini, 19 George Biagi, 20 Nicola Cattina, 21 Pablo Canavosio, 22 Giulio Toniolatti, 23 Riccardo Bocchino.
Ospreys: 15 Richard Fussell, 14 Tommy Bowe, 13 Andrew Bishop, 12 James Hook, 11 Nikki Walker, 10 Dan Biggar, 9 Rhys Webb, 8 Jonathan Thomas, 7 Marty Holah, 6 Justin Tipuric, 5 Alun Wyn Jones (capt), 4 Ryan Jones, 3 Adam Jones, 2 Richard Hibbard, 1 Paul James.
Replacements: 16 Huw Bennett, 17 Ryan Bevington, 18 Duncan Jones, 19 Ian Gough, 20 Tom Smith 21 Tom Isaacs, 22 Ashley Beck, 23 Sonny Parker.
Referee: Andy Macpherson (SRU)
Assistant referees: Alan Falzone (Italy), Filippo Bertelli (Italy)