The victory takes Milan within four points of leaders Juventus, who visit Cagliari on Saturday, while third-placed Inter are now five points adrift of Milan.

There are four rounds of matches to be played after this weekend's fixtures.

"It was an important win for us," said Milan coach Carlo Ancelotti. "We have extended our lead over Inter and need to keep that in the coming games."

Milan's Alberto Gilardino and Inter's Luis Figo missed good chances as they sent headers wide from promising positions but neither team looked sharp going forward in a rather flat game.

The decisive goal came when Milan's Dutch midfielder Clarence Seedorf looped in a high cross from the left and with the Inter defence stationary Kaladze chested the ball down and blasted past Inter keeper Julio Cesar.

Despite a 74,000 crowd there was an unusually subdued atmosphere in the San Siro, largely due to a boycott by Inter fans who left their section of the north stand largely empty.

The 'ultras' were protesting against a disappointing season and in place of the colourful flags that normally fill their sector, banners criticising the team were displayed in front of empty seating.

It took only 10 minutes for bad news to reach Inter coach Roberto Mancini when Serbian defender Sinisa Mihajlovic limped off with a muscle problem and was replaced by Marco Materazzi.

Gilardino should have put Milan ahead in the 16th minute when Cafu chipped a cross to him in the area but the Italy striker's diving header was embarrassingly wide.

After the break Seedorf had a low shot blocked by the feet of Julio Cesar and on the hour Inter's best chance was wasted by Figo, who was picked out by Dejan Stankovic but produced a poor header that went harmlessly wide.

Milan rarely looked in trouble after Kaladze's goal as they took revenge for a 3-2 defeat by Inter earlier this season but Mancini felt his team deserved something out of the game.

"I think 1-1 would have been a fairer reflection of the match. In the first half, playing with five men in midfield and just Adriano up front, we were better than Milan," he said.

However, Mancini has virtually given up on second place.

"All we have left now is to finish the season in the spirit of fair play and go for the Italian Cup," he said.