Wholesale changes from Luciano Spalletti backfired at San Siro – Serie C minnows Pordenone well worthy of taking the game to extra time after a laboured Inter squandered a glut of chances.

Indeed, it could have been better for the visitor had stand-in goalkeeper Padelli not managed to turn Simone Magnaghi's rasping first-half strike onto the woodwork.

Substitutes Marcelo Brozovic and Ivan Perisic injected intensity into Inter's play, though both spurned golden opportunities to beat the superb Simone Perilli.

Mauro Icardi was introduced as Spalletti's final roll of the dice, but even Inter's free-scoring captain could not correct their profligacy in front of goal as Pordenone held firm to reach spot-kicks.

However, the fairy tale ended there as – despite the best attempts of Perilli – Nagatomo stepped up to convert the winning penalty after Padelli had denied Giulio Parodi in sudden death.

Pordenone had to ride its luck at times and, having already kept out Eder Martin's stinging drive, Perilli came to his side's rescue again with just over 20 minutes played, rushing out to thwart Yann Karamoh.

Inter's failure to convert their early dominance into a goal almost proved costly on the half-hour mark as, moments after Giovanni Formiconi just failed to round off a well-worked set-piece routine, Padelli tipped Magnaghi's thunderous strike onto the upright.

While Luca Lulli also went close for Pordenone, Inter should have been ahead on the stroke of half-time, but Karamoh could only lash over when one-on-one with Perilli.

Spalletti had seen enough, Andrea Pinamonti making way for first-team mainstay Brozovic at the restart – and the playmaker should have done better when teed up by Karamoh.

Pordenone was quick to remind Inter of its threat as Miguel Maza went close with a strike that deflected agonisingly wide off Roberto Gagliardini.

Perisic was Spalletti's next change but he, like Brozovic, passed up an immediate chance to put Inter ahead when he nudged wide from Joao Cancelo's cross.

Inter finally looked set to take the lead in the 86th minute, but Icardi – Spalletti's final substitute – could not head home to avoid the additional 30 minutes.

Icardi got through again in the early stages of extra time, only to shoot wide under pressure from Perilli.

Pordenone's goalkeeper was finally beaten in the 104th minute, but Icardi's header, which looked destined for the bottom-left corner, crashed off the post.

Perisic wasted the chance to atone for his earlier miss when he got through just after the restart, thumping a venomous effort into the side-netting as Pordenone survived to take it to penalties.

But Pordenone's dreams came to an end in a dramatic shoot-out as, in spite of two excellent saves from Perilli, it was his counterpart Padelli who did the damage.

Inter's goalkeeper brilliantly kept out Parodi's attempt and defender Nagatomo maintained his cool to send Spalletti's side into the last eight, with the relief evident.