Inter Milan brushed off their poor league form to stun Serie A leaders Napoli 2-0 in the Italian Cup quarter-finals on Tuesday night.

Two defeats and just four points from their last four league matches have seen Inter lose command of Serie A and drop to third, four points behind Napoli.

But goals from Stevan Jovetic and Adem Ljajic at the San Paolo stadium in Naples saw Inter through to the semi-finals, where they will face the winners of Wednesday's last quarter-final between Lazio and champions Juventus.

Inter's city rivals AC Milan will play third division Alessandria in the last four. The minnows won 2-1 at second tier Spezia on Monday night while Milan defeated Carpi last week by the same score.

Tuesday's match was a tight affair, in part due to Napoli coach Maurizio Sarri leaving top scorer Gonzalo Higuain on the bench.

Despite 20 goals in 20 games this season, the Argentina striker didn't enter the fray until the 72nd minute but just two minutes later, Inter struck.

Montenegro international Jovetic, a summer signing from Manchester City, hit an unstoppable shot that left Napoli goalkeeper Pepe Reina rooted to the spot.

Two minutes from time, Napoli had Dries Mertens dismissed and in time added on, Serbian Ljajic sprinted 50 yards to score the killer second on the counter-attack.

That goal sparked a furious touchline altercation between Sarri and Inter boss Roberto Mancini.

The semi-finals will be played over two legs on January 27 and March 2.