Spurs fielded a much-changed lineup against the Baggies following their goalless draw against Partizan earlier in the week but still looked sluggish for most of the game.
Following the loss, Pochettino told reporters: "It's not an excuse. We played with 10 different players from the game against Partizan in Belgrade on Thursday. I believe that we were in a good condition to play the game today and to have a good game with a good performance but it is strange that we played very slow.
"I think the beginning of the game was wrong. We were very slow, we moved the ball very slowly, and we had a very slow tempo.
"In football you need to play quickly because the opponents sometimes, like West Brom today, play a bit deeper. You have to try to recover the ball and be aggressive in offensive situations."
The result left Tottenham ninth in the Premier League table.