Siena earned their first away victory of the season in spectacular fashion, but Genoa are shamed by a dismal performance.
These two teams were without a win in their last seven games, so the pressure was very much on. Francesco Bega sat out a ban for the home side, but Matteo Paro and Ivan Juric returned from suspension.
The visitors had a surprisingly strong start with Rubinho parrying Paul Codrea's free kick and then both Massimo Maccarone and Simone Vergassola failed to make the most of Paolo De Ceglie's assist.
Siena took a shock lead after just 11 minutes, as Mario Frick ran on to a wonderful searching pass over the defence from Daniele Galloppa that the Liechtenstein international smacked in with his left foot.
Incredibly it was 2-0 by the 20th minute, as the Genoa defence was static on a corner kick and gave Simone Loria all the time he needed to thump home the loose ball from six yards.
Genoa simply crumbled and were 3-0 down. Massimo Maccarone waltzed into the box and although his angled drive was saved, there was nobody to close down Frick for the follow-up.
These were desperate times, so Coach Gian Piero Gasperini made a tactical change after 27 minutes and it made an immediate impact. Marco Borriello and Marco Di Vaio's efforts skimmed the woodwork, while Alex Manninger beat away a powerful Julio Cesar Leon strike.
Instead Siena risked a fourth with Galloppa's effort from the edge of the box skimming the crossbar.
After the break Manninger parried a Leon snapshot and managed to get his body in the way of Borriello's follow-up. Genoa tried to fight back, but the damage had been done and they rarely troubled Manninger.
Only substitute Figueroa got a consolation goal in stoppages as he gathered from Di Vaio and fired under the bar.