The talismanic Swede marked his return to first-team matters with a spotkick, while their Bari native scored a fine goal of his own, as the Italians earn a first European win
A second-half penalty from the former Barcelona hitman and a delicate Antonio Cassano chip were enough for the Serie A holders to prosper on the night, but they had to firstly overcome a resolute Plzen side, who were not prepared to back down and lose their unbeaten record in Europe this season without a fight.
The match began very openly, with Plzen setting their stall from the first minute. The visitors had started their Champions League campaign in reasonable fashion, drawing 1-1 against BATE Borisov on the first matchday, and they looked to capitalise on the break at every opportunity.
Meanwhile, Massimiliano Allegri's side seemed buoyant with the return of Ibrahimovic in their ranks, but his comeback possibly overshadowed the impact of his team-mates initially, as the talismanic Swede was central to virtually every attack at the Czech's goal.
However, it was Plzen who had the game's first chance, and it needed a save from the top drawer from Christian Abbiati to deny Vaclav Pilar's bullet header inside the third minute. Unsurprisingly, Milan began to dominate the possession, as their contrasting playing styles made for a fascinating state of affairs.
Milan continued to search for a breakthrough, and they came mightily close through the feet of Ibrahimovic, who profitted from Cassano missing his header at the far post, but his powerful strike could only find the hands of Marek Cech, who pulled off a marvellous stop from close range.
Plzen proceeded to have an equally-perilous opportunity of their own, as Pavel Horvath blazed over a free shot at goal inside the Milan box near the end of the first half, with Abbiati seemingly in no-man's land.
However, the second half was a stark contrast to the first 45, as Milan stepped up several notches and broke the deadlock on 53 minutes, as Marian Cisovsky's handball lead to a penalty, and Ibrahimovic netted the spotkick with ease, sending Cech the wrong way.
The Italian champions doubled their lead through a counter-attack 13 minutes later, as Ibrahimovic once again led the way with an inch-perfect through ball to Cassano, who finished with aplomb, cutely lifting the ball over an onrushing Cech.
A late raid of sorts at the Milan goal ensued from Pavel Urba's men, but the wall of Alessandro Nesta and Thiago Silva continued to stand for the remainder of proceedings, coupled with the hosts' impressively cohesive football on display, as Milan earned the first victory of their Champions League Group H campaign.