Albion manager Micky Adams cut short Michel Kuipers' debut because he wasn't doing his job.
The big Dutch goalkeeper got the chop just 45 minutes into Saturday's opening 2-0 defeat at Southend.
Kuipers, a close season capture from Bristol Rovers on a free transfer, was not injured and Adams described the change as "tactical."
He said: "If people don't do the job I expect them to they won't be on the pitch."
Adams also took off captain Paul Rogers at half time to bring on Darren Freeman and change the formation after Albion fell behind to Martin Carruthers' early header.
Mark Cartwright, Kuipers' replacement, made two fine saves but could do nothing to prevent David Lee clinching victory for Southend late on.
Cartwright, signed on a month's loan from Wrexham last week, admitted he was surprised to get his chance. "I didn't think Michel had that much to do or that he had done that much wrong, but it's the gaffer's opinion that counts.
"Corky (Alan Cork) just told me to try and speed things up a bit and get the lads going again. I had a lot to do and I enjoyed it, although I didn't enjoy the result."
Adams said: "A few silly people will look at the League table and see we are in the lower echelons, but that doesn't matter. Our pride has been hurt and our 14-game unbeaten run from last season has come to an end, but so what? It's not the end of the world.
"We'll have to put another run together now. I believe my players are capable of doing that. I've got a thing about not losing the faith and I am asking supporters not to lose theirs.
"We are all disappointed at letting 3,500 fans down, but I can assure them we will get better."
Bobby Zamora had few opportunities to shine following his £100,000 move from Bristol Rovers. Paul Watson picked up an ankle injury in the second half and so did summer signing Lee Steele after replacing Gary Hart.
Albion face Rochdale in their first home fixture at Withdean on Saturday. Adams added: "I'm not downhearted. It's a long season. We will lick our wounds and come back fighting."
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