West Brom manager Roberto Di Matteo admitted his injury-depleted defence could not cope with Fulham's aerial power at Craven Cottage on Tuesday night.
After Scott Carson had failed to deal with Simon Davies' 30-yard strike just before the interval, Clint Dempsey and Brede Hangeland both scored with headers as Fulham sealed a 3-0 win.
Di Matteo said: "We knew we were up against a big side today and we are missing five centre-halves and we don't quite have the resources to put an 11 out that could handle Fulham tonight. They were bigger than us tonight and they took advantage of it."
He added: "We have been OK on corners and set-pieces but in the last three games we have conceded and that is creeping in a bit."
Carson's mistake set Fulham on the road to victory. The England goalkeeper got both hands to Davies' strike but could only deflect it into his own net.
"Scott is disappointed. He probably could have done better. He knows that. He is big enough to know that," said Di Matteo.
Fulham's victory lifted them six places out of the relegation zone - but the Baggies' slump continued. A fifth straight defeat is their worst run of results in six years.
"Everybody's mood is a little bit down at the moment. We have had a bad run. We are a little bit down but we have to keep going, we have to pick ourselves up," said Di Matteo.
"There are a lot of clubs fighting relegation. As a newly promoted club we knew we'd be in for a tough season. We are trying to give ourselves the best chance."
Fulham and West Brom are level on 22 points and the bottom eight in the Premier League are separated by just four points.