In what was an entertaining third-round clash, Callum Robinson put the Baggies ahead early in the second half.
But Albion's hopes of securing a Premier League scalp were dealt a huge blow when Cedric Kipre received his marching orders following two yellow cards in the space of just a few minutes.
Shortly after the red, Jakub Moder pulled the visitors level before Neal Maupay won the tie in extra time.
Kipre’s red card was Albion’s sixth in 12 games – with the centre-back joining Sam Johnstone and Alex Mowatt in being suspended for next weekend’s trip to QPR.
Before the game, Ismael said he was looking forward to seeing his side test themselves against top-flight opposition – with the boss naming the strongest side he could for the visit of the Seagulls.
And he was pleased with how his team did before the red card.
“Until the red card it was a great performance – exactly as we wanted,” Ismael said.
“It was all about the performance, our intensity, our philosophy, our way to play and I think until the red card we did it perfectly against a strong Premier League side.
“We were stable but the red card was a game-changer. That is what I said to the guys after the game.
“I’m delighted with the performance, the attitude, our way. We showed all the work we have done in the seven months I have been here so far.
“But we have to cut out the red cards because it’s the same story week-in, week-out.
“We are punishing ourselves. We are not getting our rewards because with 11 guys we are able to keep clean sheets.
“And we have punished ourselves for the game next week because now we have three players suspended.
“I need to have the possibility to pick the best players in my squad and at the minute due to covid, due to injury, due to injuries we are not able to play with all the players.
“Now the money time is coming you need to play with a strong team, we need to understand that we cannot afford to punish ourselves.”