Lazio's first league defeat since the opening day meant second-placed AC Milan cut the gap to two points and leapfrogged champions Inter Milan with a 3-2 win at bottom side Bari.
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Roma, runners-up last season but inconsistent this term, were without suspended captain Francesco Totti but edged in front on 52 minutes after Stephan Lichtsteiner handled Simplicio's shot in the box.
Mirko Vucinic netted Roma's second penalty three minutes from time after Andre Dias upended Julio Baptista.
"We've been doing a bit better but hope this win gives us more of a push," Vucinic, whose side moved seventh, told Sky TV.
Milan made a quick start on Italy's heel when captain Massimo Ambrosini, returning after a month out injured, headed in fellow midfielder Clarence Seedorf's cross.
Midfielder Mathieu Flamini, one of the fringe players brought in, increased Milan's lead on 30 minutes after Zlatan Ibrahimovic had been given far too much space to set him up.
Bari impressed in their first campaign back but second-season syndrome is beginning to strike despite Vitali Kutuzov and Paulo Barreto scoring either side of Pato's third.
The Rossoneri still have tactical issues to sort but Inter's shaky form and lengthy injury list, with defender Walter Samuel set to miss the rest of the season due to a knee problem, means Milan fans are starting to dream of a first scudetto since 2004.
