AC Milan put in an assured performance at the Artemio Franchi to secure a 4-1 victory against Siena on Sunday and keep up the pressure on league leaders Juventus.Goals from Antonio Cassano and Zlatan Ibrahimovic seemed to have killed off the contest after just half an hour, but Erjon Bogdani's late consolation made for an uneasy ending to the encounter. However, Antonio Nocerino and Ibrahimovic scored at the death to round off an impressive win.The match started in favour of Milan, who from the offset showed an intent to take the match to Siena. The early signs suggested that they were keen to dictate the pace of the encounter. However, the hosts were prepared to counter the threat with high pressing and their own brand of stylish football.The Rossoneri dominated possession in the opening stages, and on 14 minutes they were presented with their first real chance, which also coincided with Zlatan Ibrahimovic's first foray into the Siena box. However he fired just wide of the target after being fed by Cassano.The Italy international was involved in most of his side's good work in front of goal, as he looked to link up with a red-and-black jersey almost everytime he had the ball at his feet, and his first half display will have delighted Azzurri fans ahead of Euro 2012.Kevin-Prince Boateng was next up for Milan, as he used his power at the far post to rattle the crossbar with a looping header, but he was expertly played offside by a resilient Bianconeri defence. However, the warning signs had been coming, and shortly after, the visitors broke their duck.A cross from Ibrahimovic appeared to have been stopped by Siena goalkeeper Zeljko Brkic, but the Udinese loanee spilled the ball at Cassano's mercy, as the forward tapped into an empty goal to give his side the lead on 26 minutes.And just three minutes later, the roles had reversed. This time it was Cassano who laid off Ibrahimovic, and the Swede shrugged off a Siena jersey, before taking a touch and slamming the ball past Brkic to effectively put the result to bed.For all of Siena's endeavour, bar the odd sight of goal from Mattia Destro and Marcelo Larrondo, they failed to provide a true goal threat to Christian Abbiati, and the second half was much of the same, as the match began to fizzle out.Milan were more than happy to see out their commanding lead, but an uneventful 20 minutes suddenly saw Destro squander a creditable chance for the hosts. However, he failed to make a sweet connection with Luca Rossettini's pinpoint deep cross.Ibrahimovic tried to hit back with a pair of long-range efforts, but Brkic was equal every time in the Siena goal. Nevertheless, Milan did not look like giving up victory as the match drew to a close.However, out of the blue, with seven minutes to go, Siena netted a late consolation through substitute Bogdani, who already showed his mettle with a couple of earlier moves as he slid home a rebound from Destro's earlier effort.But the win was sealed by Nocerino, who capitalised on a mistake in midfield on the stroke of 90 minutes to power an electric strike into the back of the net, before Ibrahimovic made it 26 for the season with a cool finish past Brkic, courtesy of another Cassano assist.The win keeps Milan three points behind Juventus with three Serie A matches remaining, while Siena drop to 13th in the league standings.