Nacer Chadli had looked to earn the Baggies all three points against his former side, only for the England star to convert from close range in the 89th minute
A late Dele Alli equaliser gifted Tottenham a 1-1 draw with West Brom after Nacer Chadli's strike against his former club had looked to have given Tony Pulis' men victory at The Hawthorns.
Alli calmly slotted beyond the sprawling Ben Foster from eight yards out in the 89th minute to rescue a point for Spurs, who remain the only undefeated side in the Premier League this season, after Chadli had given the Baggies the lead just seven minutes earlier.
Chadli smashed high into the roof of the net after Hugo Lloris had expertly saved from James McClean, but he was muted in his celebration against the team that sold him in August.
The game had appeared to be heading to a stalemate after an inspired performance from West Brom goalkeeper Ben Foster, who saved superbly from Alli, Christian Eriksen and Ben Davies as Spurs lay siege to the West Brom goal at the end of the first half.
Albion had offered little by way of an attacking threat before Chadli's late intervention, though Salomon Rondon wasted a chance to convert from five yards out in first half stoppage time.
Mauricio Pochettino's men are now unbeaten in their opening eight league games thanks to Alli's late equaliser, the first time Spurs have managed that in 26 years.
But Pochettino will be concerned as Toby Alderweireld left the pitch on a stretcher ahead of Tuesday's Champions League trip to play Bayer Leverkusen.
It is now four games unbeaten for the Baggies as they continue their solid start to the season and Pulis will be heartened too by the substitute return of Chris Brunt after an eight-month injury lay-off.
The game's pattern was apparent from the outset, with West Brom happy to surrender possession to their visitors and wait for an opportunity to counter.
West Brom's disciplined defence frustrated Spurs in the early stages, limiting them to speculative shots from distance. Foster held a dipping Eriksen effort after 15 minutes, then avies' first-time strike was deflected behind.
But Spurs burst into life on the half hour and only the heroics of Foster kept the score goalless.
First, the West Brom goalkeeper was called into action to smother at the feet of Alli as the ball broke to him in a crowded penalty area, before getting down smartly to palm away a firmly struck Davies drive three minutes later.
His best series of saves came as the game neared half-time, diving low to his left to block an Alli strike as the England international finally breached the West Brom backline and raced clear on goal, and then somehow clawing away a low Eriksen shot from the edge of the area that looked destined to nestle in the bottom corner.
West Brom fans were forced to wait until first-half stoppage time for their first opening, a fine double save from Lloris denying McClean's left-footed strike and Rondon's close-range follow-up.
West Brom started the second half with more attacking intent, but Gareth McAuley could not quite react quickly enough as a corner rebounded to him in the penalty area, the ball bouncing off his thigh, and Spurs were able to hack to safety.
Alderweireld was taken off after 56 minutes following an awkward landing as he duelled for an aerial ball with Rondon, causing a lengthy break in play.
Five minutes later, a wicked deflection turned a wild Moussa Sissoko strike just inches wide of the post at the other end of the field as Spurs ramped up the pressure once more.
But it was West Brom who broke the deadlock after 81 minutes, as they began to apply pressure on Spurs from a series of corners. McClean fired on goal and Lloris got down swiftly to his left to parry inside his near post, but the rebound fell to Chadli, who launched it beyond the French goalkeeper's despairing dive.
Tottenham were not finished there, though, as lovely hold-up play by substitute Son Heung-min down the left flank eventually found Alli inside the penalty area eight yards from goal and he took a touch and coolly slotted it beyond Foster to snatch a point for Spurs.