The Baggies headed to the bet365 Stadium as record-breakers having avoided defeat in their first 10 league games of the season.
But that record ended at match 11 with Stoke running out of deserved winners in the Potteries.
In truth, the hosts should have won by a much bigger scoreline with Michael O’Neill’s side missing a number of clear-cut chances while striker Sam Surridge saw a penalty saved by Sam Johnstone.
And Ismael believes tiredness was one reason his side underperformed with the boss saying they will come back strong when they face Blues after the international break.
“I don’t know if it was tiredness but the most important thing to say is that Stoke were better tonight,” the Frenchman said.
“Stoke are the best team we have played so far.
“We made too many mistakes. That is the big reason.
“And when you start to make a lot of mistakes like that it’s a sign of tiredness.
“I think in the performance we lost some energy because we weren’t clinical in the pocket, we lost too many balls.
“We didn’t create a lot of chances. We had some chances to score.
“But in games like this you need to put in a performance and that is what we will learn - that an average performance won’t be enough in this league.
“When you are average someone will come from behind and take your spot.
“We accept tonight that the opponent was better, we were not good enough.”
“We need to take the defeat and learn from it.
“We go into the break to recover and when we come back we will come back strong for the game against Birmingham.”