Alan Pardew admitted Bournemouth's last minute winner was a bitter pill to swallow.
Albion looked to be ending their run of defeats after Jay Rodriguez had given the visitors the lead just after half time.
But the Baggies again failed to hang on to a lead when Jordan Ibe fired past Ben Foster in the 77th minute.
Junior Stanislas then curled home a free kick in the 89th minute to give the Cherries an undeserved victory.
"It's really difficult to take," said Pardew after the game.
"It's heartbreaking for everyone - the fans, the staff and particularly the players, who did not deserve that.
"The gameplan and the execution of the gameplan I could have no complaints about.
"It's very difficult to talk to the players after an effort like that - their application and their fight was commendable.
"They did not deserve that outcome, they really didn't."