With top-flight leaders Inter Milan easing into the last eight with a 3-0 home victory over second tier Cagliari, Alessandria stole the limelight by following up their win over Palermo in the last round with another upset.
Their fairytale evening threatened to turn sour when Leonardo Pavoletti equalised for Genoa in the second minute of stoppage time after Manuel Marras had given Alessandria the lead a minute into the second half.
Riccardo Bocalon, however, latched on to a Marras pass to score in the 114th minute and ensure the visitors became the first third tier side since Bari in 1983/84 to reach the last eight.
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The defeat heaps more pressure on Genoa coach Gian Piero Gasperini with his side also fourth from bottom in Serie A having lost their last three league games.
In contrast to Genoa, Inter's passage into the next round was straightforward.
Argentine Rodrigo Palacio opened the scoring with a tap in after 24 minutes, his first goal in 12 games this season for Inter, before Marcelo Brozovic and Ivan Perisic were on target in the second half.
Holders Juventus meet Torino in a Turin derby on Wednesday when AS Roma face second tier Spezia, Fiorentina play Carpi and Napoli take on Verona.
On Thursday, Lazio host Udinese and Sampdoria welcome AC Milan.
(Writing by Toby Davis; Editing by Tony Jimenez)
