Tony Pulis admitted his disappointment at Gareth McAuley's defensive lapse cost the Baggies at Stamford Bridge.
Albion had held firm against title chasing Chelsea until McAuley's slip let in Diego Costa to score the goal's only game.
But Baggies boss Pulis was quick to move on from the error and instead focused on the positivies.
"I was happy all the way through the game," said Pulis.
"They play a different system to most teams and we'd worked on a structure to beat them.
"It's disappointing because Gareth has got to deal with it. He's made a mistake and we move on. We don't really want to criticise anyone. Our structure and organisation was very good.
"One mistake, one chance and the fella puts it away - that's the difference in quality that separates the teams at the top."
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