The Baggies continued their unbeaten start to the league campaign thanks to a last-gasp Semi Ajayi strike that broke the hearts of their hosts.
The defender, making his first start of the season, struck in the fourth minute of stoppage time when he tapped in his first goal of the season after being picked out by Matt Phillips’ cut-back.
Ajayi was a relieved man having earlier slammed an effort against a post just before the hour after debutant substitute Jordan Hugill’s header was saved. Albion also had two penalty appeals dismissed during an action-packed second period before Ajayi settled the issue.
Manager Ismael was booked by referee James Linington for joining in the wild celebrations following his side’s goal and he then became involved in a post-match bust-up with members of the Posh bench.
Ferguson accused Ismael of making an offensive gesture in the aftermath, but the Frenchman was at pains to stress the incident was a misunderstanding.
An angry Ferguson said: “I don’t mind him celebrating. They can do that all they want and it’s nothing to do with me.
“But I don’t like people being disrespectful and you need to shake another manager’s hand – not give them the ‘Vs’ after the game.
“Did they expect us just to roll over to them? They didn’t like it when they got a bit back.
“He’s managing a big club like West Brom and behaved like that. He needs to calm down the guy. He’s reached one play-offs – he’s no Pep Guardiola!
“We were magnificent to a man and went toe-to-toe with West Brom all the way to the 94th minute.
“They are a difficult team due to the manner of how they play, but they didn’t have too many clear-cut chances and we dealt with everything they threw at us.
“I can’t do anything other than compliment the performance of my players and it is such a cruel way to lose a game.
“I really feel for the lads as they didn’t deserve to be beaten.”
Ismael insisted he was not being disrespectful
The former Barnsley boss said: “He (Ferguson) misunderstood. I went to the fourth official and gestured that we should have had two penalties. I think he misunderstood my gesture.
“It has been explained to me that in England it means something different. That was not my purpose. It was not disrespectful, it was misunderstood.
“Emotion is what we missed last year. Everyone was at home but this is football. It’s a great feeling when you win.
“It doesn’t matter that I got yellow carded. I would be happy to get one every game if we win.
“The last-minute winner is the most emotional in football and means a lot. Such a win will bind an emotional connection between the staff, fans and club.
“I’m really pleased for Semi. It’s not easy when you’re not playing but I’ve told everyone they will play a part.
“It was a difficult game and a difficult week as we got a lot of injuries and we knew it would be a tough game.
“We started well and managed all the situations and kept a clean sheet. We showed the desire to score but some games are like that.
“You can’t always score three or four goals to win, but it’s important to stay strong and win the duels and the second balls.”