Southampton were made to pay for fluffing their lines as Antonio Candreva's second-half strike secured a much-needed Europa League victory for Inter Milan.
Jay Rodriguez went close to opening the scoring in the first-half at the San Siro but was excellently thwarted by Samir Handanovic, while the Saints striker also saw a second-half header disallowed for a foul.
And the Italian side, who were without a victory in Group K going into this clash, took advantage when Candreva steamed a left-footed piledriver past Fraser Forster and in off the underside of the crossbar.