Boss Dean Smith admitted Aston Villa blew their chance after being knocked out of the Carabao Cup by Stoke.
Sam Vokes sent the Potters through to the quarter-finals as Villa's second-string suffered a 1-0 fourth-round defeat.
Henri Lansbury and Keinan Davis missed Villa's best chances as last season's beaten finalists failed to find a way past their Sky Bet Championship visitors.
Villa rested captain Jack Grealish with Smith making 11 changes, and they slipped up.
"It's a massive missed opportunity and I said that to the players. I don't often get into them at half-time but I did today because we were that poor in the first half," said Smith.
"With the tempo we played at it was a lacklustre first half and an awful performance. The first-half performance was way below the standards.
"We got rewarded (at Bristol City) last week and rightly so. What I expected was a similar performance but we were too lacklustre and made too many mistakes on the ball.
"There weren't too many surprises from Stoke, the biggest surprise was how slow we were on the ball."
Stoke edged the first half and grabbed the winner from their first serious attack of the game.
Jed Steer turned over Nick Powell's rising drive, and from Jordan Thompson's resulting corner Vokes glanced in after 26 minutes.
Stoke have kept six clean sheets in their opening seven games – including their 1-0 Carabao Cup win at Wolves – but benefitted from poor Villa finishing.
Lansbury blew a golden chance to level four minutes after Vokes' winner when he headed wide from five yards.
Just before the break Davis stabbed wide at the far post as Villa continued to stumble.
They improved after the break but Stoke could have doubled their lead only for Vokes to plant a free header wide.
Adam Davies saved from Anwar El Ghazi and Ollie Watkins and the Potters survived late pressure to book their spot in the last eight.
"It was a really good performance, I'm delighted. We handled the game really well," said boss Michael O'Neill
"It gives us a bit of confidence going into Sunday's game (against Birmingham)
"It's a nice situation to be in, we haven't got a lot to lose but they managed it really well.
"It's a good test for us to come to places like Villa and Wolves and keep clean sheets. The cup has been a very worthwhile competition for us because we have a big squad and we can utilise it.
"We had more of the play than we had against Wolves. We got ourselves ahead, the shape of the team was good and we handled it well."