Son bemoans 'soft' Spurs for 'unacceptable' defeat to West Ham
Ange Postecoglou's team raced out of the blocks at the start of the campaign, playing a dazzling brand of attacking football and winning eight of their first 10 games to top the table.
But their momentum has slowed dramatically in recent weeks and they now find themselves nine points behind leaders and bitter London rivals Arsenal.
Spurs came into the match in buoyant mood after an enthralling 3-3 weekend draw against champions Manchester City and they started in style at the Tottenham Hotspur Stadium.
Cristian Romero put the home side ahead early, just reward for their dominance, but the visitors equalised through Jarrod Bowen shortly after half-time and James Ward-Prowse completed the turnaround in the 74th minute.
Delighted West Ham manager David Moyes said his side had the ability to give top sides a "bloody nose".
"Huge performance because of the quality of the opposition," he told Amazon Prime. "We were up against it tonight. We had to dig in. Thankfully we just about scraped it.
"The quality Tottenham showed in the first half, I don't know if we touched the ball for eight or nine minutes."
Spurs on top
Spurs enjoyed around 90 per cent possession in the opening minutes as the visitors struggled to make any sort of impact.
They got the reward they deserved in the 11th minute when Romero met an outswinging corner from Pedro Porro and guided his header into the top corner from the centre of the penalty box.
The home team continued to dominate and create chances, with Dejan Kulusevski catching the eye.
Giovani Lo Celso's shot in the 35th minute was saved by Lukasz Fabianski before Brennan Johnson fired straight at the goalkeeper.
But Spurs failed to make their overwhelming superiority count and were grateful when Lucas Paqueta headed wide after a fine cross from Mohammed Kudus in the closing minutes of the first half.
Spurs nearly doubled their lead on the stroke of half-time when Lo Celso's cross was deflected onto the stanchion by West Ham captain Kurt Zouma.
But the second period was a different story, with West Ham dangerous on the break and Spurs' energy levels dipping.
England forward Bowen battled to win the ball on the left and fed Kudus, whose shot was deflected into Bowen's path and he made no mistake to level in the 52nd minute - scoring for the seventh away game in a row in the league.
Spurs substitute Richarlison came agonisingly close to levelling with his first touch but his header was inches wide of the back post.
Instead, it was West Ham who scored next, taking advantage of a defensive calamity.
Destiny Udogie played a back pass back to goalkeeper Guglielmo Vicario but it was short and Vicario could only parry it away to Ward-Prowse, who hit the post but tucked the rebound into an empty net.
It means for the fifth game running Spurs failed to win after scoring first - losing four and winning one of those games.
Spurs captain Son Heung-min pleaded with his team to be more ruthless.
"You get the lead five times in a row and losing the game is unacceptable," he said.
"We were soft and especially in the Premier League, even if you're winning 2-0 or 3-0 you never know what's going to happen in the end. One-nil isn't enough, you have to try to kill the game."
The defeat leaves Spurs in fifth spot, three points outside the top four, while West Ham are ninth.