Inter Milan came from behind to beat reigning champions Barcelona 3-1 on Tuesday at home in the Champions League semi-final first leg match.

Inter beat Barca in Champions League semis first leg.

Pedro gave Barca an early lead, only for Inter to hit back powerfully with goals from Wesley Sneijder, Maicon and Diego Milito.

Barca left complaining about Portuguese referee Olegario Benquerenca over the last goal from Milito, which was regarded as an offside goal.

It was the first time in his highly successful reign as Barca coach that Pep Guardiola's team has lost by more than one goal, and it means that they will have to beat the Italians by at least two goals in next Wednesday's second leg in the Camp Nou.

Barca will be without captain Carles Puyol, who picked up another yellow card in Milan.

In the 20th minute the Catalans took the lead. Maxwell, playing against his former team, broke free down the left and centerd cleverly for Pedro, who scored from just behind the penalty spot with his left foot.

Inter equalized just 10 minutes later. Ex-Barca idol Samuel Eto 'o, placed by coach Jose Mourinho on the right wing, centerd for Milito. The Argentine opened to the left for Sneijder, who beat Victor Valdes with a near-post drive.

Right-back Maicon made it 2-1 for Inter three minutes into the second half after another quick break that Milito created into a clear chance.

Inter continued to play on the break and Milito scored what could turn out to be a crucial third goal in the 61st minute.

Sneijder headed the ball down and Milito headed home from what looked like an offside position.

Barca looked tired in the second half, possibly as a result of their two-day coach journey to Milan, caused by Europe's air traffic ban for the Iceland's volcanic ash.