ROBERTO Di Matteo was 'angry and disappointed' with Albion's early second-half defending which allowed Bristol City to come from behind and win 2-1 at Ashton Gate.
Top scorer Graham Dorrans' 25th-minute opener - his 13th of the season - gave the visitors a deserved half-time lead.
But Albion came apart at the seams after conceding on-loan Wolves striker Chris Iwelumo's equaliser from a corner ten minutes after the break, which Di Matteo felt turned the game in City's favour.
And the head coach's frustration mounted four minutes later as his side fell foul to a Robins counter-attack rounded off by Lee Johnson's winner.
"I am disappointed and angry because we wanted to get a positive result here," said Di Matteo.
"Once you're in the driving seat, it's really disappointing to give it away.
"We were quite comfortable until they equalised.
"At 1-0, you are always a bit concerned because the opposition can score.
"We knew the next goal would be an important one.
"I don't think they were threatening much before they scored from the corner.
"We should have defended better and made it more difficult for the opposition to score.
"To concede from a set-piece is disappointing.
"It gave them confidence and lifted the crowd.
"I thought the game changed a little bit after they equalised because up to that point we were quite comfortable.
"Conceding within the space of five minutes after that was very bad.
"Danny Haynes caused us a few problems with his pace but it was poor that we got countered on, especially away from home.
"But the equaliser was the most important goal in this game.
"Had they not scored from a set-piece, they would have had to work very hard to get a goal.
"We had a few half chances to equalise but didn't quite manage to create clear-cut opportunities to level."
The Baggies' first away defeat in five months meant they missed out on at least the point that would have taken them back to second in the table on goal difference above Nottingham Forest.
But they still remain in a strong position, with a game in hand over Billy Davies' men.
Di Matteo added: "We don't like to lose and I don't think we should have lost today - but credit to Bristol.
"Let's hope we can rebound and show our full strength.
"We'll talk about this game and analyse the mistakes we've made.
"But there is not much time because the next game is coming up on Wednesday."