The Orica-GreenEDGE speedster beat Manuel Belletti (AG2R-La Mondiale) and Gerald Ciolek (MTN Qhubeka) to the line in a bunch sprint in driving rain at the end of a 232km stage from San Vincenzo to Indicatore (Arezzo).
The Omega Pharma-QuickStep lead-out train lost position in the run-in to the line and Mark Cavendish had to settle for fifth, behind nemesis Roberto Ferrari (Lampre-Merida), but the British star retains the overall lead after his Belgian squad won Wednesday's opening team time trial.
Kevin Hulsmans (Vini Fantini-Selle Italia) instigated an early attack and was joined by Cesare Benedetti (NetApp-Endura) and Garikoitz Bravo (Euskatel).
They lead by seven minutes following the first two categorised climbs of the race at Massa Marittima after 44km and Cantoniera Montebello after 85km.
With 95km to go, their advantage peaked at 8:30 but that quickly diminished as the stage concludes with five, mostly flat 12.4km circuits around Indicatore.
The escapees were caught with 27.5km to go to set up the inevitable gallop to the line.
Cavendish was looking for a repeat victory after winning over the same route in last year’s race but it was BMC, Lotto and GreenEDGE on the front in dangerous conditions as they went under the Flamme Rouge.
And it was 26-year-old Tasmanian who took the victory and completed a World Tour double for his Australian team after Michael Albasini had won at Paris-Nice less than an hour before.
Goss said: “In the sprint, Peter Sagan came from behind. He’d come from a long way back but I knew he’d go anyway, and I kind of timed my sprint on his.
“This is my first road race in Europe this season and I’ve won, so I’m looking forward to the rest of the season now. I know if I’m in good shape I can do a good Milan-Sanremo next week. It’s definitely a goal for me.
“It’s always nice to win. It doesn’t really matter who’s second or third. Cavendish and Andre Greipel are two guys I’ve sprinted against, and been in the same team as. Last year I couldn’t get the upper hand. Hopefully I can turn a lot of last year’s second places into wins.”
The top five places on GC all remain in the possession of Omega Pharma-QuickStep but Cavendish was unhappy that his team did not put him in a better position in the run-in to the line.
He said: “I was 30 riders back in the final kilometre and I had a lot of work to do. With 200m to go the peloton went right and I had to slam the brakes on, and that was when I lost.
“We worked as a team but we weren’t in a good position in the final kilometre. I’m disappointed with my lead out. I know they’re better than that. We’ll have words tonight.”