Slaven Bilic admitted Albion were second best against Middlesborough as the Baggies lost their 14-game unbeaten run following a 2-0 defeat.
Goals from Daniel Ayala and Ashley Fletcher gave Boro their first away victory of the season - and inflicted Albion's first home defeat of the season.
The Baggies, who gave starts to Gareth Barry and Kyle Edwards in midfield, struggled to find any sort of rhythm and looked sluggish throughout.
"We've got to pick ourselves up and come back as soon as possible to where we were a few weeks ago," Billic told BBC WM 95.6 after the final whistle.
"Are we a little bit tired? Yes, we are. But the whole league is a little bit tired. We have to get that freshness back. A few of the games recently we haven't started well enough.
"The good news is that we have a big game, massive game (against Leeds) in a couple of days' time. It's a great opportunity for us in front of the home crowd to make up for what we missed today.
"It's an ideal game to show the character, to show the quality, to show the determination, basically to show everything."