Stoke manager Mark Robins said his team had been given a reality check at Queens Park Rangers.
Harvey Vale's second-half goal earned a 1-0 win for the hosts as the Potters fell to their first away defeat of the season.
Robins told BBC Radio Stoke: "That's the worst we've played this season. We have to maintain a level and maintain our non-negotiables, and we just didn't.
"We got exactly what we deserved, so it's back to the drawing board. Optimism is fantastic but unless you do things right all the time, and not just when you fancy it, you are going to come unstuck.