Inter held off Frosinone's second-half fightback to strengthen their position inside Serie A's top four thanks to Sunday's 3-1 win at Stadio Benito Stirpe.
Goals from Radja Nainggolan and Ivan Perisic before the interval appeared to put Luciano Spalletti's side on course for a routine victory over their relegation-threatened hosts.
But Francesco Cassata halved the deficit just past the hour with an effort that Inter goalkeeper Samir Handanovic ought to have repelled.
That strike breathed fresh life into the contest as the Nerazzurri were forced to hold on somewhat grimly for the remainder, ultimately securing a success that cements their place in third thanks to Matias Vecino's injury-time strike.