Giampaolo Pazzini, on his first start since undergoing knee surgery last season, and Robinho also got on the score-sheet as the club began life without Massimiliano Allegri
Robinho opened the scoring before Giampaolo Pazzini and Keisuke Honda, both on their first starts this season in Rossoneri colours, added to the scoreline before Nicola Ferrari got a consolation for the visitors.
The Serie A outfit have struggled this season but there was no evidence of this on Wednesday as they brushed aside an inferior Spezia.
With Massimilano Allegri sacked on Monday and incoming coach Clarence Seedorf not on the bench, it was left to Mauro Tassotti to oversee the comfortable victory.
Philippe Mexes attempted a long-range effort that drifted narrowly over the bar early on as Milan got used to life after Allegri. That effort set the tone for the game with the Rossoneri looking comfortable against the Serie B outfit.
Pazzini was keen to make an impact having been afforded a rare starting opportunity for Milan after undergoing knee surgery to his right knee at the end of last season.
The striker was heavily involved in proceedings and could have put the Rossoneri ahead early during the first half, but perhaps still a bit rusty from the lengthy lay-off he wasted a couple of chances that fell to him.
However, the attacker then provided Robinho with an opportunity to score and the Brazilian made no mistake, diving low to head Milan in front.
The Rossoneri doubled their lead minutes later as Pazzini made amends for his earlier missed opportunities, showing his instinctive prowess to let the ball drop over his shoulder before firing a well-timed volley beyond Juventus-owned Nicola Leali in Spezia's goal.
Spezia came close to halving the deficit, however, when Riccardo Montolivo had to react to clear Andrea Bovo's goal-bound header off the line shortly before half-time.
But it was Milan who further extended the lead when Honda took advantage by following up from Montolivo's effort, which squirmed out of the clutches of Leali.
The hosts had further chances to extend the lead through Pazzini, who should have had a hat-trick, but it was Spezia who grabbed a late consolation when Ferrari took advantage of Christian Abbiati's parried save.