Parma put the boot into 10-man Milan
Parma's forward Antonio Cassano celebrates after scoring a penalty during the Serie A football match between AC Milan and Parma at San Siro Stadium in Milan on March 16, 2014 - by Giuseppe Cacace
After two consecutive defeats the pressure was on Milan coach Clarence Seedorf, who in midweek was forced to deny he had had harsh words for misfiring striker Mario Balotelli.
But despite the misfortune of seeing 'keeper Christian Abbiati sent off inside 10 minutes for a foul on Ezequiel Schelotto, the burden on the 37-year-old Dutchman is now likely to weigh heavier.
Milan's third defeat in succession, following reverses to Juventus and Udinese, left the ailing Italian giants 37 points behind leaders Juventus and now 11 behind Parma, who occupy the first Europa League spot in fifth.
While Juve continue their charge towards a third consecutive scudetto -- they hold a 14-point lead on Roma, who have a game in hand, before their respective games later -- the battle for European places is well and truly on.
Parma now have a one-point lead on Fiorentina as well as a game in hand, although Fiorentina can reclaim fifth spot with a win at home to Chievo later on Sunday.
The visitors were well on their way to an upset when Abbiati was shown a straight red card for a blatant foul on Schelotto and former Real Madrid, Milan and Inter striker Cassano stepped up to beat Marco Amelia from the spot in the ninth minute.
Seedorf reshuffled and Milan did well to soak up the pressure for the remainder of the half.
But only six minutes after the restart Cassano, unmarked on the edge of the Milan box, controlled Afriyie Acquah's angled ball to beat Amelia for Parma's second.
Seedorf replaced left-back Urby Emanuelson with Adil Rami and five minutes later the big France defender rose above the Parma defence to head Kaka's corner past Antonio Mirante.
When Joel Obi was adjudged to have fouled Riccardo Montolivo, somewhat harshly, with just over 15 minutes remaining and Balotelli scored with a stop-start spot-kick, the fightback looked on.
But only two minutes later Milan's defence was left despondent after former Inter man Schelotto got the ball across to Amauri to flick with his heel past Amelia.
Amelia did well to block Schelotto's effort with his legs but the 'keeper could not keep out Jonathan Biabiany's diving header in the fifth minute of added-on time as the ball ricocheted in the area.
Elsewhere, Lazio maintained their hopes of Europa League football with a 2-0 away win at Cagliari which kept the capital side five points behind Parma in seventh.
Relegation-threatened Livorno had two men sent off but survived to beat Bologna 2-1 at home and move one point clear of the relegation zone.
In another bottom-of-the-table clash Sassuolo beat Catania 3-1 to send the Sicilians back to the bottom.
Fiorentina host Chievo and Juve travel to Genoa in Sunday's late games while Napoli, in third, are away to Torino on Monday, when Roma host Udinese.