
On 51 points from 24 games, the Rome side can further reduce the gap when they visit Inter in a midweek round, while third-place Juventus were held on 47 points as they crashed to a 2-1 defeat Saturday at lowly Reggina.
Brazilian Cicinho flicked home a close-range chance for Roma's crucial win, while Inter had to thank the seldom fielded Hernan Crespo for equalizing Samp's opening goal from Antonio Cassano.
Cicinho, who was dismissed with two minutes left, had come close with a fierce drive during a first half that saw Fiorentina lose mainstay forward Adrian Mutu to a serious injury.
The Romanian hurt his knee as Doni blocked his break in the area, and was replaced by Senegal's Papa Waigo. Fiorentina had their best chance when Swiss Zdravko Kuzmanovic shook the woodwork as Roma controlled the second half, coming close through a spurt from captain Francesco Totti.
In Genoa, the in-form Cassano stunned Julio Cesar with a shot, and in the remaining 25 minutes Inter pressed forward looking to preserve their unbeaten record.
The goal finally came in the 76th minute on a header from Hernan Crespo.
"It was a difficult game because Samp at home had won (their last three games), and also because we came from a Champions League game (at Liverpool)," Inter coach Roberto Mancini said.
"We fell behind and fought back to clinch an important draw. In the second half, we did better than in the first, during which we had a harder time."
Things were brighter for cross-town AC Milan, who late Sunday drew level with fourth-place Fiorentina on 41 points as veteran Filippo Inzaghi nodded home a late header to clinch a 2-1 win over visiting Palermo.
In earlier action, Marco Borriello had a great time in Udine as he scored a hat-trick to help Genoa win 5-3 at sixth-place Udinese. The young striker, who is jointly owned by Milan, is now the league's best scorer on 15 goals next to Juve's David Trezeguet.
Atalanta drew 2-2 with struggling Siena, coming from behind through a brace from Sergio Floccari. Emanuele Calaio also scored a brace as Napoli won 2-1 at Livorno, and Empoli steered clear of the danger zone beating Catania 2-0.
Bottom side Cagliari won 1-0 at home with 10 men against mid-table Lazio. Reggina are second-last despite their win over Juventus and trail Parma, who drew 4-4 Saturday at Torino.
By Alberto Cagliano, dpa