Spurs did little to alleviate the pressure on rookie boss Tim Sherwood early on with some woeful defending allowing the home side to race into a three-goal lead without having to do a great deal.
Matej Vydra scored the fourth fastest Premier League goal of the season after just 31 seconds to break the deadlock, before returning captain Chris Brunt had all the time in the world to volley in the second just three minutes later.
Emmanuel Adebayor then missed a great chance to get Spurs back in it, but saw his tame penalty easily saved by Baggies keeper Ben Foster.
And Stephane Sessegnon punished Adebayor's miss by racing past Vlad Chiriches to net the third.
Kyle Naughton's deflected cross beat Foster to give Spurs hope before the break, and set the tone for what was a different away side in the second half.
Harry Kane deservedly put Spurs back in it from close range before Eriksen fired in a late equaliser after sustained pressure from the visitors for the whole 45 minutes.
The result still leaves Spurs with a mountain to climb if they are going to secure a top-four finish, while Pepe Mel will be wondering what he has to do to claim his first home win as West Brom boss.
It was a remarkably slow start by the visitors, who were extremely careless at the back, and were punished immediately.
Danny Rose was easily beaten down the right flank by Morgan Amalfitano, who whipped a fierce cross into the box, which Hugo Lloris could only palm into the path of Vydra, who smashed the ball into the empty net.
Albion swiftly added another, taking advantage of sloppy play at the back by Spurs as Steven Reid's cross dropped to Brunt via a flick-on and the Baggies skipper volleyed home sweetly.
Tottenham looked to hit back quickly and, after Kane had fired an attempt wide, the visitors were awarded a penalty around the quarter-hour mark when referee Neil Swarbrick ruled Amalfitano had fouled Rose in the West Brom box.
The subsequent effort from the spot by Adebayor was tame and Foster was able to get down to his left to keep it out.
Spurs had an escape in the 26th minute when Amalfitano, allowed considerable space in the area, received the ball from Youssouf Mulumbu and drilled it at Lloris, who pushed it over the bar.
However, a third soon followed, as Jonas Olsson's long hopeful ball forward from defence was headed backwards by Kaboul and taken by Sessegnon, who drove forward while holding off Chiriches before slotting beyond Lloris.
Spurs' hopes of a comeback were soon boosted. Only three minutes after Sessegnon's strike, the away side had a goal back when Olsson diverted a cross into the box past his own goalkeeper.
And moments later Foster pulled off a great double save, pushing away Paulinho's shot before denying Rose on the rebound.
Tottenham kept up the pressure after the restart and, after Rose put an attempt wide, Foster produced further heroics, palming behind an Aaron Lennon strike and then jumping to keep out a lofted Eriksen free-kick.
Rose was in the thick of the action once again when he went down in the West Brom area claiming a foul by Reid, only to pick up a booking from Swarbrick for his trouble.
Kane twice went close before getting his goal, rising to head in from Lennon's cross.
The equaliser came in dramatic circumstances as the ball came to Eriksen in the box after a cross was flicked on and the midfielder got the better of Reid before cracking the ball into the net.