Alan Irvine was left frustrated by West Brom's slack defending after they threw away a two-goal lead to lose 3-2 at QPR.
Albion made a strong start to Saturday's Premier League match at Loftus Road, with Joleon Lescott and Silvestre Varela scoring their first goals for the club to put them two goals up after 20 minutes.
Irvine's men wasted chances to increase their lead and were made to pay by Charlie Austin, who scored a hat-trick as Rangers mounted a stunning fightback to secure all three points.
Irvine was disappointed not to claim at least a point and rued poor defending from set pieces, which cost his side dear.
"We deserved to win the game and the fact that we didn't was down to us not defending well at three corners," the Albion head coach told BBC Sport.
"And not being as clinical as our play deserved because I thought we played really well in the game.
"It's bitterly disappointing to leave with nothing, I would have been disappointed with a point.
"We've been so close to getting good results week in, week out, but if we can tidy up at both ends we should be okay."
The defeat leaves Albion in 14th place, two points clear of third-bottom Burnley ahead of a Boxing Day clash with champions Manchester City at the Hawthorns.comments