Mauricio Pochettino denied Tottenham suffered a dose of the title jitters after they blew the chance to go top.
Spurs knew victory at West Ham would lift them above Leicester to the summit for the first time this season, as well as send out a huge statement in the race for the Barclays Premier League crown.
Instead Michail Antonio's early goal was enough to secure a 1-0 victory for the Hammers and bring an end to Totttenham's six-game winning streak .
But Spurs boss Pochettino said: "Was it nerves? No. We made some mistakes that normally we don't make.
"We didn't start well. The first half was poor, we never found solutions to play like we normally play.
"We had more freedom in the second half but if you don't score it's difficult to get the points.
"We were poor. We know. We are very disappointed. But the way the players fought in the second half was fantastic."
West Ham were determined not to give their fierce rivals a reason to celebrate in the final London derby under the lights at Upton Park.
The Hammers head to the Olympic Stadium next season but they will miss nights like this as their famous old ground was rocking.
Antonio will certainly miss the place - all six of his goals for West Ham this season have come at home.
The latest arrived in the seventh minute, when Dimitri Payet swung in a corner and Antonio met it with a powerful near-post header which Hugo Lloris got a hand to but could not keep out.
Tottenham, having become the masters at coming from behind this season, had plenty of time to respond - but this time they could not find a way back.
Harry Kane missed the best chance when he failed to connect with the rebound after Adrian kept out Toby Alderweireld's long-range shot.
Victory lifted the Hammers, still unbeaten at home since August, to within a point of fourth-placed Manchester City.
Manager Slaven Bilic admitted: "If we had to take one game out of the season, for the fans, then it's Spurs at home.
"To match them you have to play well, but to outplay them and win was magnificent.
"Maybe I'm biased but they should be more happy with the result than us, because it could have been more.
"In all aspects of football we were magnificent and I congratulate the players."