Rome:Ronaldinho scored his first goal in Italian football to give AC Milan a vital 1-0 victory over Inter Milan in a pulsating city derby at the San Siro.
Inter Milan had two players sent off -- although Marco Materazzi was dismissed after he'd been substituted -- as Jose Mourinho tasted defeat as Inter coach for the first time.
It means that despite losing their first two matches, Milan are right back up in the thick of the title race having won their next three in a row.
Ronaldinho dedicated his goal to the Milan fans and club president -- and Italy prime minister -- Silvio Berlusconi, who celebrates his 72nd birthday.
"I'm very happy, I was hoping to score a goal. This one is for the fans who've made me feel at home," said the Brazilian.
"It's a moment of great happiness, I know tomorrow is president Berlusconi's birthday, this goal is for him."
Previous leaders Inter drop down to fourth with the loss as the Serie A table takes on an unfamiliar look.
Lazio are the new Serie A leaders after they won 3-1 at Torino while Napoli, one of only two remaining unbeaten teams, are up to an unlikely second following their 1-0 success at Bologna.
Udinese are third having won 2-1 at home to Siena while Catania, who beat Chievo 1-0, are fifth ahead of Milan and Juventus.
In Milan Inter had more of the ball but Milan were looking dangerous on the break and on 25 minutes Kaka beat Maicon down the left before crossing for Ronaldinho, whose left foot shot was blocked by goalkeeper Julio Cesar.
Milan went in front on 36 minutes on the counter as Ronaldinho fed Kaka wide on the right before charging into the penalty area to meet his countryman's cross with a bullet header into top corner from almost on the penalty spot.
Mourinho waited less than a quarter of an hour after the break before deciding he'd seen enough and he threw on two strikers.
Brazilian Adriano and Argentine Julio Cruz came on for centre-back Materazzi and winger Alessandro Mancini in a typical Mourinho substitution.
Inter's task was made tougher when Nicolas Burdisso was sent off with a quarter of an hour left after picking up a second yellow card.
Mourinho brought on Dejan Stankovic with his final throw of the dice and he forced Milan goalkeeper Christian Abbiati into parrying a vicious volley before Adriano blasted the follow-up over the bar.
In a thrilling finale, Materazzi was shown a red card for berating the referee from the sideline and Milan substitute Andrei Shevchenko forced Julio Cesar into a fine save before Adriano headed wide from inside the six-yard box.
Mourinho refused to comment on the referee and defended his attacking substitutions.
"I don't think either side deserved to win more than the other, they scored a goal so well done Milan," he said. "I'm not talking about the referee, I want to be on the bench for the next game.
"I'm not afraid, when I'm not happy with the result I take risks. Unfortunately with 10 men I can't make more attacking changes." Lazio have been the surprise team of this season and their fourth victory in five matches ensured their place at the top.
Macedonia forward Goran Pandev and a brace from scudetto top scorer Mauro Zarate, one from the spot, put them 3-0 up before nine-man Torino scored an injury time consolation goal from a Nicolas Amoruso penalty.
Lazio coach Delio Rossi said there was still more to come from his table-toppers.
"I'm happy to be the coach of players who give their all and play to their best," he said.
"It seemed easy today but Torino played well. I thought in the first half they played better than us but for the rest of the game it was all Lazio.
"We have worked hard and this group can develop and improve as we're missing important players like (Tommaso) Rocchi and (Francesco) Matuzalem."
In the capital, last season's runners-up AS Roma won for only the second time this season in a 2-0 home success over Atalanta.
Centre-back Cristian Panucci opened the scoring through a deflected strike before Montenegro forward Mirko Vucinic added the second with a slick turn and shot.