AC Milan moved to top of the Serie A table after a hard-fought 2-0 win over Cagliari on Tuesday, while the Tuscan derby finished 0-0.
A Francesco Pisano own goal and Zlatan Ibrahimovic strike either side of half-time at Stadio Sant'Elia was enough for Massimiliano Allegri's men to secure victory against his former club.
The result ensured Milan move a point clear on top of the Serie A table, though Juventus will reclaim their lead should they defeat third-placed Udinese on Wednesday.
Thiago Ribeiro made a bright start for Genoa, firing an angled drive against the base of Christian Abbiati-s right-hand post.
But the lead soon belonged to Milan.
Ibrahimovic released Robinho with an intelligent through ball after four minutes, and the Brazilian rounded both goalkeeper Michael Agazzi and defender Michele Canini to flash a low ball across the face of goal.
Pisano could only turn into his own net, under pressure of Antonio Nocerino.
The second goal seemed inevitable and Milan got it in the 61st minute. Ibrahimovic flicked the ball to Robinho, retrieved his strike partner's headed return, before nonchalantly lifted the ball over the advancing Agazzi to make it 2-0.
Siena and Fiorentina shared the spoils in a goalless Tuscan Derby that produced five yellow cards for either side.
Siena came closest to breaking the deadlock when Emanuele Calaio hit the crossbar in the first half, while Gaetano D'Agostino's free-kick brought a fine save out of Fiorentina goalkeeper Artur Boruc.
Fiorentina boss Delio Rossi opted to leave Alberto Gilardino on the bench and it may have backfired, with visitors blunted in attack.