Jake Livermore's scrambled goal in second-half stoppage time kept Albion's improbable hopes of Premier League survival flickering but the result at the Hawthorns could also have ramifications at the other end of the table.
However, Antonio Conte's men have played a game less and can apply some pressure by beating Jurgen Klopp's Champions League finalists on Sunday.
"We fully dominated the game, but if you are not clinical in front of goal and don't score the chances you have, always it's open," he said.
"In this type of game, against this type of team like West Brom - they worked so hard on set pieces and when the game is open you can concede."
Mauricio: “It’s a cruel way to lose, but we need to accept that. We cannot change the result, we need to focus on winning the last two games and try to finish in a good way.” pic.twitter.com/Iy9gBx0D2B— Tottenham Hotspur (@SpursOfficial) May 5, 2018
Victory at Stamford Bridge at the start of April seemed to all-but settle the top-four argument from Spurs' point of view, but a run of one win in their past four league matches has Pochettino's men stuttering towards the finishing post.
"I think maybe we need to assess why," he added. "Of course the games that we played after [beating Chelsea], yes, our performance dropped a little bit.
"It looked like after Chelsea the job was done and that's why I'm disappointed in our performances in the last few weeks.
"We need to work so hard during the last two games to try to win them both because it's in our hands to be in the Champions League next season."
Pochettino confirmed centre-back Toby Alderweireld's absence against West Brom was due to a twisted ankle. The Belgium international will be assessed on Sunday.