Claudio Ranieri's Inter were pegged back in their quest to return to the top of the Serie A table as they lost 2-1 to hard-working Catania.
Esteban Cambiasso scored for the visitors in the first half, but Vincenzo Montella's men turned the tables with a three-minute double salvo from Sergio Almiron and Francesco Lodi after the break to stun the Nerazzurri.
The game got off to a thrilling start as the visitors took the lead in the fifth minute after a brilliant cross by Maicon was diverted into the net by Cambiasso, who finished on the volley from the left side of the box with his left foot.
Catania found their feet later on, however, and soon began pressing Inter in their own half. Almiron had a shot fly over the bar from outside the box, while Alejandro Gomez was causing the Nerazzurri's defence all kinds of trouble down the right wing.
Nicolas Spolli had a header from the centre of the box fly wide of the left post soon after the half-hour mark, but the hosts were still struggling to create chances in front of Luca Castellazzi.
That changed as soon as the second half began as a quick break saw Gonzalo Bergessio square to Almiron, who sent an unstoppable shot into the top right corner to level the proceedings.
Inter received yet another blow in the 50th minute, when the ex-Saint-Etienne striker broke free of the Nerazzurri's defence and left Castellazzi with nothing to do, but bring him down in the box.
Lodi converted the penalty for Catania, leaving Claudio Ranieri wondering how come his team collapsed so easily in a matter of moments. The ex-Roma man threw everything forward in search of an equaliser, but his players were struggling to break the hosts' resolute defence.
In fact, Bergessio, and later Maxi Lopez, were giving the Nerazzuri quite a headache, and nearly managed to punish Inter's leniency at the back on a couple of occasions on the counter-attack.
The introduction of Mauro Zarate and Ricardo Alvarez hardly changed anything for the visitors, who looked devout of ideas upfront. In fact, Catania nearly doubled their lead in the 75th minute, when substitute Gennaro Delvecchio was denied by Castellazzi in a one-on-one.
Inter had their goalkeeper to thank moments later, when Andrea Catellani broke free on the left, but failed to put the ball past the Nerazzurri's No.12. Claudio Ranieri gave everything they had in the final minutes of the game, but were ultimately unable to score.
Following tonight's result, Catania are sixth in the standings with nine points, while Inter are 17th, just above the relegation spots. Vincenzo Montella's men's next game is away to Fiorentina on a week, while the Nerazzurri host Chievo a day later.