MILAN - Diego Milito converted a late penalty to reach double figures as Inter edged Fiorentina in the pouring rain at the Stadio Giuseppe Meazza.
With time running out, Il Principe sent Frey the wrong way to net his tenth of the season and seal a deserved 1-0 win that sees José Mourinho's defending champions move eight points clear of the chasing pack.
The Inter coach fielded 4-3-3 against the Viola with Zanetti coming in for the suspended Maicon at right-back, Muntari in place of Thiago Motta in midfield and Quaresma up front with Eto'o behind Milito.
Viola boss Cesare Prandelli made one change to the team that beat Lyon in midweek, bringing in Comotto for De Silvestri at right-back.
After an evenly-balanced first half in which Quaresma shone for the Nerazzurri, Inter were far more dangerous than their purple-shirted opponents.
Walter Samuel thought he had put Inter in front on 50 minutes when he headed home a corner but Damato disallowed the goal for a foul by the Argentine defender on Dainelli.
Frey made saves from Lucio and Milito, who miscued along with his strike partner Eto'o as the Nerazzurri were left rueing a series of missed chances.
Fiorentina's Alberto Gilardino almost gave his team the lead against the run of play on 80 minutes, outwitting Lucio and Samuel before firing on to the post.
Inter's reward came five minutes from time, Milito rifling home from the penalty spot after being brought down by Comotto.
Eto'o missed a glorious chance to double Inter's lead in the closing stages, being denied by Frey after racing unchallenged on goal from the halfway line.
Inter 1-0 Fiorentina (HT: 0-0)
Scorers: Milito (pen) 85.
Inter: 12 Julio Cesar; 4 J.Zanetti, 6 Lucio, 25 Samuel, 26 Chivu; 5 Stankovic, 19 Cambiasso, 11 Muntari (8 Thiago Motta 73); 7 Quaresma (30 Mancini 73), 22 Milito (14 Vieira 87), 9 Eto'o.
Subs not used: 1 Toldo, 2 Cordoba, 15 Krhin, 23 Materazzi.
Coach: José Mourinho.
Fiorentina: 1 Frey; 25 Comotto, 2 Kroldrup, 3 Dainelli (29 De Silvestri 77), 19 Gobbi; 18 Montolivo, 15 C.Zanetti; 32 Marchionni (20 Jorgensen 18), 24 Santana (9 Castillo 86), 6 Vargas; 11 Gilardino.
Subs not used: 35 Avramov, 8 Jovetic, 21 Babacar, 23 Pasqual.
Coach: Cesare Prandelli.
Referee: Antonio Damato (Barletta).
Booked: Chivu 34, Gobbi 35, Kroldrup 43, C.Zanetti 67, Samuel 79, Comotto 84.