Williams, 31, said: "It's a learning curve for us but we have to pick ourselves up immediately because we've got another huge game against Leicester. We hope to have a different performance and approach to the game. We are far better than what we've shown."
While Heineken Cup kings Munster and Toulouse stride onto yet another semi-final in Europe, the Ospreys appeared lost on their first visit to the quarter-final stage. And Williams admits that despite having 11 of Wales's Grand Slam winning side among their ranks, they froze on the big occasion.
Williams added: "Disappointment is a huge understatement - we threw it away. Infact, it wasn't a performance at all. It was very disappointing and we made a lot of mistakes in crucial areas.