Ospreys made a lacklustre start to their RaboDirect Pro12 defence with an indisciplined defeat away to Treviso at the Stadio Comunale di Monigo.
Wales lock Ian Evans was sent off on 31 minutes for two yellow cards, the first for interfering at a ruck and the second for a dangerous tackle.
Treviso full-back Kris Burton punished the indiscretions with four penalties.
Ospreys improved in the second half but had to settle for a losing bonus point from Dan Biggar's two penalties.
The fly-half was wide with three other attempts at goal, while the Welsh side also butchered a handful of decent try opportunities.
Centre Ashley Beck was held up over the line after seeming to be tripped, Biggar opted to go inside from a break with Hanno Dirksen screaming for the ball on the right wing, while Richard Fussell's loose pass snuffed out an overlap on the left.
Admittedly the handling conditions were extremely difficult, after torrential rain in northern Italy had left parts of the pitch with deep puddles.
Evans saw his first yellow card for knocking the ball out of a Treviso player's hands while prone under a ruck, while his second came for a high tackle not long after he had returned to the pitch.
The Italians had Ignacio Fernandez-Rouyet and Dean Budd sin-binned, but Ospreys will rue not being able to take advantage and suffering their first defeat to an Italian team.
Treviso: Kristopher Burton; Ludovico Nitoglia, Tommaso Iannone, Alberto Sgarbi, Luke McLean; Alberto Di Bernardo, Edoardo Gori; Alberto De Marchi, Enrico Ceccato, Ignacio Fernandez-Rouyet, Francesco Minto, Corniel Van Zyl (capt), Simone Favaro, Alessandro Zanni, Robert Barbieri.
Replacements: Franco Sbaraglini for Ceccato (56), Michele Rizzo for De Marchi (57), Lorenzo Cittadini, Dean Budd for van Zyl (57), Paul Derbyshire for Favaro (70), Marco Filippucci for Barbieri (57), Fabio Semenzato for McLean (65), Brendan Williams.
Sin Bin: Rouyet (45), Budd (61).
Ospreys: Richard Fussell; Hanno Dirksen, Andrew Bishop, Ashley Beck, Tom Isaacs; Dan Biggar, Kahn Fotuali'i; Ryan Bevington, Richard Hibbard, Aaron Jarvis, Alun Wyn Jones (capt), Ian Evans, James King, Sam Lewis, Jonathan Thomas.
Replacements: Scott Baldwin, Duncan Jones for Bevington (67), Joe Rees, Joe Bearman for Lewis (67), Morgan Allen, Rhys Webb for Fotuali'i (69), Matthew Morgan for Biggar (75), Tom Grabham for Isaacs (75).
Sin Bin: Evans (9).
Sent Off: Evans (31).
Referee: John Lacey (IRFU).
Assistant Referees: Giuseppe Vivarini, Andrea Spadoni (both FIR).
Citing Commissioner: Roberto Carra (FIR).
TMO: Alan Falzone (FIR).