Ospreys forwards coach Jonathan Humphreys blamed a lack of discipline and poor execution for his side's opening Pro12 loss.
The Welsh region suffered a shock 12-6 defeat in a rain soaked Stadio Comunale di Monigo against Treviso on Friday.
Thw visitors were forced to play the majority of the match a man short after Ian Evans was sent off following two first-half yellow cards.
"We're very disappointed tonight, with the first half in particular," said Humphreys.
"Our discipline let us down and we went out there and did everything we'd said pre-match that we wouldn't do, allowing them to build a lead with three, six, nine points.
"We were well aware that it was going to be tough but when you aren't at your best and are lacking discipline then you make life very difficult for yourself and that was definitely the case tonight. They made us pay dearly.
"We wanted to get off to a winning start and we haven't done that.
"We know that we came up short tonight and we've got to work hard over the next seven days to make sure we perform better against Ulster at the Liberty Stadium in front of our own fans next weekend."