Goals from Kevin-Prince Boateng and Sulley Muntari saw off the Catalan giants, but it was the Rossoneri's defending that Allegri was particularly pleased with.
"I’m very happy, it was an extraordinary game from a defensive point of view as we didn’t concede anything to Barcelona. We slipped up on a couple of passes but in the second half the team did well," he told reporters.
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The 45-year-old Italian is confident about Milan's future, and he singled out striker Giampaolo Pazzini for praise.
"The team is still growing it’s doing so very quickly, I think it’s a team that will do well for years to come. Pazzini played an extraordinary game and he’s shown that he’s a great player at a European level," he continued.
With the Milan derby on Sunday and the return leg at Camp Nou under three weeks away, Allegri was quick to point out that there is no point getting carried away.
He added: "We haven’t done anything yet though, we have to leave it there now as we have the derby and we have to recharge our batteries immediately.
"I’m very happy with what the players have done and we should enjoy this evening and start focusing on the derby tomorrow."