Winston Reid tapped home a 66th-minute corner from close range for the first in Sunday's Premier League clash at White Hart Lane, before Ricardo Vaz Te had a slice of luck to slot in off Spurs keeper Hugo Lloris six minutes later.
Ravel Morrison secured three points for Sam Allardyce's men when he raced clear from midfield, got between Spurs' centre halves and poked the ball in off the unfortunate Lloris in the 79th minute.
Earlier, Kevin Nolan had missed a golden opportunity to score in the first half from a well-executed West Ham free-kick, while Jermain Defoe was denied by a good block from Jussi Jaaskelainen.
A midweek trip to Russia looked to have taken the sting out of Andre Villas-Boas' side, who lacked a cutting edge throughout, while despite being underdogs, West Ham had the better of the opening exchanges.
Mohamed Diame sneaked into the Tottenham box, but Jan Vertonghen and Paulinho did just enough to put the midfielder off. Stewart Downing then whipped in a cross from wide, but Kevin Nolan could only head wide.
Spurs were restricted to long shots for most of the opening half hour as Tomkins and Reid performed well to keep Defoe and Christian Eriksen quiet.
Andros Townsend seemed to be the only Tottenham player capable of causing any problems. The winger slalomed past his marker and played a clever ball into Gylfi Sigurdsson, but Jaaskelainen saved the forward's low drive. Townsend could not draw a save out of the Finn though, as he cracked a 25-yard effort just wide.
At the other end, Reid wasted a glorious chance to put the Hammers ahead when he nodded Mark Noble's corner wide when free in the box. Noble then chipped over the wall to tee up Nolan, but his volley trickled inches wide.
That proved to be something of a wake-up call for Tottenham, who started the second half brightly.
Defoe, making his first league start of the year, finally managed to get in behind the Hammers defence, but Jaaskelainen came off his line to smother the striker's shot.
Vaz Te and Morrison shot wide as West Ham came into the game, and then the away side took the lead. Nolan unwittingly cleared Reid's goalbound header off the Spurs line, but the New Zealand defender swept home the rebound.
Six minutes later, the away end was in uproar again as West Ham made it 2-0. Noble carved open the Spurs defence with a beautiful pass to send Vaz Te through. His shot rebounded off Lloris' legs and he slid the ball home.
Spurs then amazingly slipped 3-0 behind after a fantastic solo goal from Morrison. The former Manchester United man picked the ball up just inside his own half and drifted past Michael Dawson before lifting the ball over Lloris.
Tottenham fans started to leave in their droves, realising there was no way back. The away fans, in contrast, sang "we want more" and Allardyce disappointingly asked the fourth official "is that all?" when he revealed there would be four minutes of added time.
The win moves West Ham up to 13th in the table, five points behind sixth-placed Spurs after seven games.