Harry Kane scored on his return from injury for Tottenham but his side fell to a surprise 2-1 defeat at Burnley, which severely dented their Premier League title hopes on Saturday.
Ashley Barnes' 83rd minute winner for Burnley extended their unbeaten run to eight games and moved the Clarets up to 13th place in the league.
But for third-placed Spurs, who trail leaders Manchester City and Liverpool by five points, this may prove to be a loss that leaves them with too much ground to make up.
Burnley took the lead in the 57th minute with a glancing header by striker Chris Wood from a Dwight McNeil corner.
But eight minutes later Kane, playing his first game since he suffered an ankle injury on Jan. 13, ran on to a quick throw-in from Danny Rose and slipped the ball past Tom Heaton.
The Clarets, who have been in or around the relegation zone for most of the season, grabbed the winner though when substitute Johann Berg Gudmundsson found Barnes at the back post and the striker fired in his fourth goal in as many games.
Pochettino had seen victory over Burnley as imperative to his side's hopes of maintaining a title challenge.
Yet the usually affable Argentine ended up cutting an angry, frustrated figure at the whistle, confronting referee Mike Dean over what he clearly felt had been an incorrect decision that led to Burnley's first goal after 57 minutes.
Spurs had been claiming a goalkick after Jeff Hendrick appeared to touch the ball last before it went out of play but, instead, a corner was awarded to Burnley which resulted in Wood heading home Dwight McNeil's delivery.
England captain Kane, back after six weeks out with an ankle injury, responded with goal after latching on to a quick Danny Rose throw-in before Barnes notched an 83rd-minute winner, prompting Pochettino to become embroiled in a face-to- face confrontation with Dean.
"You know how important was the game and when you feel so disappointed and upset, you make some mistakes," he said.
"We made some mistakes on the pitch and I made some mistakes afterwards on the pitch. I need to go to the dressing room and drink some water but what happened, happened."
He seemed resigned that Spurs' title hopes were now over.
"If we didn't win, we cannot put pressure and we cannot think now of being a real contender. It is a massive opportunity lost for us," he said.
But Crystal Palace's Roy Hodgson was left beaming as he became the oldest man to take charge of a Premier League match at the age of 71 years, 198 days - and marked the occasion with a 4-1 win at Leicester City.
While Pochettino lost his composure, Hodgson was all smiles after his Palace side won at Leicester with a double from Wilfried Zaha, Michy Batshuayi's first goal for the club and a Luka Milivojevic penalty.
At the other end of the table, Aaron Mooy's Huddersfield Town's freefall towards the second-tier Championship hurtled on when the league's bottom club lost 2-0 at Newcastle United.
Newcastle, with a third straight home win under Rafa Benitez, moved up to 15th, two points behind 14th-placed Burnley and Palace, 13th.
In a remarkable match in the south coast featuring three penalties, Joshua King scored one and missed another for Bournemouth while Wolverhampton Wanderers earned a 1-1 draw with Raul Jimenez's 83rd-minute spot-kick.