Esteban Cambiasso scored the winning goal Wednesday to give Inter Milan a 2-1 victory over Chelsea in the round-of-16 match in the Champions League.
Inter forward Diego Milito put his team 1-0 up in the third minute before Salomon Kalou equalized for Chelsea in the 51st.
But Cambiasso hit the winner three minutes later at the San Siro, firing a left-footed strike past goalkeeper Petr Cech after his initial shot had rebounded back to the Argentine midfielder off a Chelsea player.
It was Inter coach Jose Mourinho's first competitive game against Chelsea since leaving the English club in 2007.
Kalou had a penalty appeal waved away toward the end of the first half.
The second leg is at Stamford Bridge on March 16.
Inter quickly found its rhythm. Thiago Milito slipped a pass to Samuel Eto'o, the Cameroonian miscontrolled the ball, but it ran into Milito's path and the Argentine swept a low shot inside Cech's near post.
Chelsea's first chance came in the 12th. Kalou found space on the edge of the area, but Inter keeper Julio Cesar saved his effort.
Didier Drogba hit the bar from a freekick in the 15th and three minutes later Cesar stopped Michael Ballack's shot from the edge of the box.
On the stroke of halftime Chelsea thought it should have had a penalty. Kalou raced into the penalty area and claimed he was brought down by Walter Samuel, but referee Manuel Gonzalez ignored Chelsea's appeals.
Shortly after halftime Chelsea was level. Branislav Ivanovic raced down the right before cutting across the Inter area. He laid the ball back to Kalou and the Ivorian curled a shot past Cesar from the edge of the box.
Inter retook the lead four minutes later. Sneijder crossed from the left, Cambiasso shot once and hit Ivanovic, but the rebound fell to the Argentine and he shot low into the corner of the goal.
Chelsea lost Cech in the 60th, when he was stretched off after landing badly having taken an innocuous looking catch.
Frank Lampard squandered an excellent chance to score Chelsea's second in the 65th, Nicolas Anelka linked with Drogba to send in a low cross, but the midfielder hit a poor shot that Cesar blocked.
