Lukaku's goal puts Napoli back on top of Serie A

Also on Sunday, Fiorentina won 2-0 at Como for their seventh consecutive victory and Lazio beat 10-man Bologna 3-0.

Lukaku redirected in a cross from Napoli captain Giovanni Di Lorenzo early in the second half.

Roma had a chance to equalise but Artem Dovbyk's header banged off the crossbar.

Lukaku played for Roma last season but was one of the main transfer targets when Antonio Conte was hired at Napoli for this season.

Ranieri was hired 10 days ago as Roma's third coach of the season, replacing the fired Ivan Juric, who had in turn replaced Daniele De Rossi.

Still, Roma remained in 12th place, four points above the relegation zone.

Yacine Adli put Fiorentina ahead with a long-range strike early on. Then Moise Kean redirected in a cross midway through the second half for his ninth goal of the season.

Fiorentina last won seven straight in a single Serie A campaign in 1960, when they won eight in a row.

Bologna were reduced to 10 men when Tommaso Pobega picked up two yellows during the first half.

But it took a while until Lazio took control with second-half goals from Samuel Gigot, Mattia Zaccagni and Fisayo Dele-Bashiru.

Patrick Vieira's debut as Genoa coach was a 2-2 draw with Cagliari.

Both of Cagliari's goals came on penalties, including Roberto Piccoli's equaliser in the 88th.

Vieira was hired on Wednesday to replace the fired Alberto Gilardino.

Mario Balotelli came on late for Genoa and didn't make an impact.

Torino and Monza drew 1-1.