Diego's 10th-minute strike looked to have set the Bianconeri on their way to a much-needed victory at the San Siro.

But Lucio levelled after 72 minutes and Mario Balotelli grabbed a last-gasp winner for Inter to secure a two-legged last-four date with Fiorentina next month.

Ferrara's side headed into this encounter on the back of five defeats in six Serie A games and lying in sixth position in the standings - 16 points adrift of league leaders Inter.

Despite their poor recent run, the visitors started well and broke the deadlock after just 10 minutes. Diego cut inside Esteban Cambiasso and lashed a low shot through the legs of Inter goalkeeper Francesco, who should have done better.

Jose Mourinho's team had a fine chance to get back on level terms 10 minutes later but Maicon fired over from a tight angle after a neat one-two with Goran Pandev.

The influential Wesley Sneijder then nicked possession and instigated an attack which resulted in an opportunity for Balotelli, but he could only shoot straight at Gianluigi Buffon from 18 yards.

Toldo, making only his second appearance of the season between the posts, went some way to making amends for his early error eight minutes before the break by getting down well to keep out a fierce shot from Fabio Grosso eight minutes before half-time.

The hosts had an appeal for a penalty turned down in the 44th minute when Thiago Motta's cross looked to be handled by Felipe Melo, but referee Antonio Damato was not convinced.

Juve went within a whisker of doubling their advantage 10 minutes into the second period, Giorgio Chiellini skimming the outside of Toldo's left-hand post with a far-post header from Diego's cross.

And the Old Lady were soon made to pay for that near miss when parity was restored 18 minutes from time.

Buffon was left wrong-footed when Sneijder's free-kick took a wicked deflection, and Lucio nipped in at the far post to prod home the equaliser.

The Juve stopper kept his side on level terms after 84 minutes by parrying another Sneijder free-kick, but was powerless to prevent Inter's winner at the death.

Buffon did keep out Thiago Motta's initial effort but Balotelli was on hand to capitalise from the rebound.