West Brom boss Sam Allardyce admitted he was stunned to see his side's performance in their 5-0 defeat to Leeds United.
The Whites were rampant in the game, going 4-0 up before half-time after being given the lead by a calamitous own goal from Romaine Sawyers.
Goals from Ezgjan Alioski, Jack Harrison and Rodrigo rounded off an impressive first-half performance before Raphinha's fine goal midway through the second half completed the scoring.
Allardyce cut a shocked figure on the touchline, looking furious at how his side had collapsed.
The Baggies' performance was at odds with how they performed at league leaders Liverpool on Sunday, frustrating the reigning champions as they came from behind to draw 1-1 after packing men behind the ball.
Allardyce admitted his side had tried to open themselves and get further forward against Leeds but the plan backfired.
Speaking to Amazon, Allardyce said his side never recovered from Sawyers' disastrous own goal, when he brushed the ball into an empty net after not noticing goalkeeper Sam Johnstone was out of his goal.
"Things can happen like that," Allardyce said of his side's own goal. "We don't expect them to happen but when they do happen you have to pick yourself up and fight.
"When we appear to play the bigger sides, not that Leeds are not a good side, but we defended well against Liverpool.
"Here when we try and open ourselves up we can't do the defending right.
"Leeds ended up with a 5-0 win and deservedly so. I was shocked to see a poor performance like that from us.
"Because we defended well at Liverpool and for long period we were better but we were terrible as we tried to open ourselves up."
