Bath's hopes of reaching the Heineken Cup quarter-finals suffered a major blow when Treviso outplayed them for large periods to seal a shock home win.
HEINEKEN CUP Pool Two
Treviso: (19) 29:
Tries: Canale, Goosen
Cons: Goosen 2
Pens: Goosen 5
Bath: (3) 23:
Tries: Barnes, Walshe
Cons: Barkley 2
Pen: Barkley 3
Bath did pick up a bonus point after rallying from a 19-3 deficit with tries from David Barnes and Nick Walshe.
But that late effort was not enough to beat a well-drilled Italian side, which disrupted the visitors from the start.
Gonzalo Canale crashed through missed tackles by Matt Perry and Brendon Daniel to set Treviso on their way.
Bath responded, centre Olly Barkley slotting his only first-half shot at goal between the uprights after the hosts dragged down a menacing Bath rolling maul.
After the restart, Barkley reduced the arrears with his second penalty, but seven minutes later the game's defining moment held the visitors back.
Bath centre Alex Crockett beat two men to race away and touch down triumphantly at the corner, but the move was in vain because the referee spotted an infringement by prop Duncan Bell.
"The referee and one touch judge made a call which triggered a 10-point swing away from us," said Bath coach John Connolly.
"Their full-back collided with Duncan Bell and made a meal of it and the touch judge's flag went up for the penalty.
"Instead of getting a try and possibly a conversion to get us back into the
match we ended up conceding another three points when they kicked the penalty."
Their momentum affected, the Zurich Premiership outfit rallied, but ultimately fell short in their bid to salvage a victory.
"We knew Treviso were a good side and we just didn't turn up in the first half," said Connolly.
"We can have no complaints about the defeat. We didn't play well and they were the better side.
"They put us under pressure everywhere and forced us into making mistakes and conceding penalties.
"Three of them, all kicked, were given against us for front row infringements in the scrum.
"It was a similar situation to the one in Montferrand last season when an Irish referee penalised the same way in similar circumstances."
Treviso: Williams; Visentin, Pozzebon, Goosen, Canale; Smith, Troncon; Faliva, Ongaro, Costanzo; Klerck, Gritti; Pavanello, Orlando, Palmer
Replacements: Picone, Sbaraglini, Dal Maso, Carpente, Parisse, Pablo Mauro, Tekeda
Bath: Perry; Crockett, Tindall, Barkley, Daniel; Malone, Walshe; Barnes, Mears, Bell; Borthwick, Fidler; Beattie, Scaysbrook, Delve
Replacements: Stevens, Grewcock, Lewis, Baxter, Davey, Lipman.