(CNN) -- Italian champions Inter Milan suffered their first defeat of the season as an injury time goal from Mirko Vucinic gave Roma a last-gasp 1-0 win on Saturday night.
The match in the Stadio Olimpico looked headed for a goalless draw until Montenegro international Vucinic popped up to score the winner.
He came off the bench to meet Daniel De Rossi's cross with a diving header to give Roma their first win of the season and put the brakes on Inter's strong start under new manager Rafael Benitez.
Champions League winners Inter have 10 points from five games but can lose their lead in the Serie A standings with Brescia and Chievo in pole position if they win their matches Sunday against Bari and Lazio.
Earlier, their arch city rivals AC Milan ended a three-match winless streak with a vital 1-0 win over Genoa in the San Siro.
Milan's Swedish international striker Zlatan Ibrahimovic wrapped up victory with a superb chip in the 49th minute.
It was his second league goal for Milan since his move from Barcelona as the victory leaves his new side just two points behind Inter.
"This win counts for a lot because it's important to be in good shape psychologically," Milan coach Massimiliano Allegri told Sky television.
"When the results don't come, you always worry, even if you're a great team."
Milan's other close season acquisition Robinho also made his first start and came close to scoring on several occasions.
But the hosts survived a scare when goalkeeper Christian Abbiati turned a Rodrigo Palacio cross onto his own far post.
He later made a superb save to keep out a Chico header, but Milan deserved their timely win.