Inter Milan extended their lead at the top of the Serie A table after defeating Genoa at Stadio Luigi Ferraris.

Inter paid a heavy price for the win, though, as they lost two key players for Wednesday's Champions League first knockout round return leg at Manchester United.

Defenders Marco Materazzi and Nicolas Burdisso both limped off in the first half and are serious doubts for midweek, although Sweden striker Ibrahimovic lasted 90 minutes on his return from injury.

Genoa set the tone of the game with a lightning start as Thiago Motta pulled a shot wide after a neat one-two with Diego Milito after just 30 seconds.

Inter then went ahead with their first attack.

Dejan Stankovic lifted the ball over the top of a Genoa defence which was slow to react to the danger, allowing Ibrahimovic to break clear and lob the ball over Rubinho to put the visitors ahead.

As the pace of the game remained high with both teams at full stretch, Inter defender Materazzi appeared to pull a muscle as he reached for the ball in the centre circle.

He left the field after 15 minutes and was followed by Burdisso on the half-hour mark as Mourinho lost both his central defenders to injury.

Ivan Cordoba replaced the former, but the Portuguese coach had no remaining defensive options after Burdisso's departure, meaning midfielder Esteban Cambiasso had to deputise in the centre of the back four.

Fortunately, Inter still had Julio Cesar in their goal and he made a world-class save to deny Motta an equaliser in the 21st minute.

Motta got enough power and direction behind his header from Giuseppe Biava's cross, but the outstanding Brazilian goalkeeper denied him before Maicon cleared the danger.

Giuseppe Sculli should have tested Julio Cesar with a free header minutes later before the Inter stopper made a double save to first deny Biava and then Milito as the home side again came close to levelling on the stroke of half-time.

The last chance of the half fell to Inter, though, with Luis Figo sending Ibrahimovic clear, but the Sweden striker was a bit slow in realising the linesman's flag had stayed down and Rubinho was able to scamper from his line and clear.

Genoa continued to dictate the play in the second half with Biava showing why he is a defender and not a striker by slicing a shot over the crossbar from 10 yards.

But the home side were hit by the sucker punch when Balotelli rounded Rubinho and sent in a weak low shot which neither Motta nor Marco Rossi were able to clear with Rossi perhaps even helping it to cross the line.

The home side tried to lift themselves, but were the victims of their own lack of incision in front of goal with Rossi and Biava the next to miss gilt-edged chances.

Genoa's first home defeat of the season and only second loss in their last 15 games dents their hopes of qualifying for the Champions League next season, while Inter's increasingly comfortable lead at the top enables them to now focus on the Champions League trip to Old Trafford.