The former Portsmouth man stunned the hosts with a hat-trick as Milan won 4-3, with the forgotten man Mario Yepes heading the winner in the 83rd minute.
Guillermo Giacomazzi headed Leece in front with the slightest of touch from a Carlos Grossmuller free-kick. Christian Abbiati, who probably should have done better with Leece's opener, conceded a penalty mid way through the first half fouling Daniele Corvia, after dropping a simple corner at the Italian's feet. Massimo Oddo, ironically on a season long loan from AC Milan, stepped up and smashed the penalty home. Grossmuller incredibly made it three just before half-time, stabbing home a lose ball.
Boateng started the comeback just four minutes into the second half with an exquisite slashed finish. A Milan corner was only half cleared and after the ball found its way to Boateng, the Ghanaian, smashed home brilliantly.
If the former Spurs midfielder's first effort was good, his second was brilliant. Teed up by the controversial Antonio Cassano, Boateng let fly with another cracking effort, giving the Leece keeper simply no chance.
Boateng amazingly levelled an amazing game in the 63rd minute, in doing so completing his hat trick. Christian Abbate saw his effort blocked and the ball fell kindly for Boateng whose shot narrowly crossed the line.
The Colombian Yepes amazingly won the game for AC in the 83rd minute with a back post header. Cassano was again the creator, as his lofted cross was met well by the former PSG defender and his bullet header won the game for the Rossoneri.
Elsewhere in Italy, unbeaten Juventus were held to their fourth draw in the opening seven games as Genoa got a deserved 2-2 away to the 'Old Lady'. A late Andrea Caracciolo strike ensured the heavy spending Genoa left with a share of the spoils.
Thiago Motta ensured Inter got only their second victory of the season as they overcame Cheivo 1-0 at the San Siro. Roma bounced back from their derby defeat with a solid if not spectacular 1-0 home success against Palermo. The Argentine Lamela scored the only goal of the game after just eight minutes.
Despite their loss of key players at the start of the season, Udinese continued their fine start to the season with a comprehensive victory over Novara. Two Antonio Di Natale strikes and one from Maurizio Domizzi were easily enough.
Fiorentina 2 Catania 2
Cagliari 0 Napoli 0
Parma 1 Atlanta 2
Siena 2 Cesena 0
Bologna 0 Lazio 2