While admitting that the result took him by surprise, O'Shea has urged his players to respond quickly to the loss.
"We were nilled at home in a match that we entered with huge expectations. We're shot to pieces because we certainly didn't see that coming. In emotional terms that's a big blow," he is quoted as saying by ESPN.
"We have to react to that. We can talk about it all we like, but we have to respond. We'll find that very difficult to take, but we have to take it. It's an incredible emotional low. We didn't see it coming. We won't read the players the riot act for something like that. It's sport and sometimes you come across things you can't explain."
Harlequins return to action on next Saturday when they host London Wasps in the league.