Hugo Lloris put on another goalkeeping wonder-show on the continent, saving Radamel Falcao's early penalty and somehow diverting Kamil Glik's thumping close-range volley over the bar with a flailing arm as the Ligue 1 side looked to extend their advantage in the closing stages.
But his awesome resistance alone wasn't enough for us as Sidibe headed home just after the interval with Monaco carrying over their attacking threat from the first period into the second.
And merely 38 seconds after Harry Kane hauled us back level from the penalty spot, Lemar angled one in from the left side to seal the win for the Group E leaders.
The result leaves us with four points from our five games in the competition and, although we could feasibly draw level with second-placed Bayer Leverkusen on matchday six on December 7, the German side would still progress on the head-to-head rule after their 1-0 win at Wembley earlier this month.
Mauricio Pochettino made four changes from our win against West Ham United at the weekend most, notably at the back. There was a Champions League debut for Kevin Wimmer in central defence as Jan Vertonghen dropped to the bench along with Kyle Walker, who was replaced at right-back by Kieran Trippier. In midfield, Dele Alli and Heung-Min Son also came back in for Christian Eriksen and Vincent Janssen.
CHANCE: SON THROUGH ONE-ON-ONE – 6mins
The game started with a great tempo and we should have grabbed an early lead as the first clear-cut opening went begging. Alli stepped in from the right-hand side and weighted a perfect through ball that allowed Son to beat the off-side trap and run clean through on goal. With only Danijel Subasic to beat, the South Korean international opted to go around him but the keeper forced him wide and the chance was wasted.
PENALTY SAVE: LLORIS TO THE RESCUE – 11mins
The drama continued with action at the other end as the home team this time missed the chance to go ahead from the spot. We made a mess of clearing a bouncing loose ball in the box and Eric Dier swung a boot at it but caught Fabinho on the shin. A penalty was given, Falcao stepped up to take it, hitting it low to Lloris' right but there was our captain to claw the ball away. We remained largely on the back foot for the rest of the half and Monaco almost went ahead when Valere Germain galloped free in the right channel and fizzed a shot inches past the foot of the post.
Above: Kevin Wimmer up against Bernardo Silva.
GOAL: MONACO 1-0 SPURS – DJIBRIL SIDIBE - 48mins
Monaco didn’t take long after the restart to take the lead. The lively Benjamin Mendy turned inside his man and fired a dangerous cross into the box for Sidibe to thump a header past Lloris from close range.
GOAL: MONACO 1-1 SPURS – HARRY KANE (PEN) - 51mins
We grabbed a leveller just three minutes after Monaco's opener from the penalty spot. Alli chased a ball into the box and as he turned he was brought down by Glik. Kane made no mistake from 12 yards with his third penalty in as many games to open his Champions League account.
GOAL: MONACO 2-1 SPURS – THOMAS LEMAR - 52mins
Before we would touch the ball again we were behind once more. Straight from the kick-off Monaco worked the ball into space on the right and Sidibe curled across goal and out to the opposite flank. Lemar, cutting in from the left, gratefully collected the ball and steered a shot low into the far corner from an acute angle.
SAVE: INCREDIBLE INTERVENTION BY LLORIS – 68mins
There was little that Lloris could have done about either goal but he pulled off another incredible save midway through the second half. Glik met a cross from the right with a powerful volley from point-blank range and our captain showed incredible reactions to somehow tip the ball over the bar. Lloris also saved well from Falcao moments later, although two chances came our way as Eriksen had a shot deflected behind and Dier saw his header - which appeared to be heading just wide - cleared from the resulting corner. There would be one final chance for us in the closing moments as Kane's shot was saved and, from substitute Christian Eriksen's resulting corner, Alli - under pressure - couldn't steer the ball on target at the back post.
MAURICIO POCHETTINO SAID
"I’m very disappointed in the way we conceded. The first half was open, we created some chances but Hugo kept us in the game. In the second half we conceded after three minutes, then we came back but in the next action, we conceded. It’s true we’re much, much better than we’ve showed in the Champions League but we need to learn that to compete in the Premier League and Champions League demands a lot of mental energy and that’s our challenge for the future."
Monaco (4-3-3): Subasic; Sidibe, Glik, Jemerson, Mendy; Fabinho, Bakayoko, Lemar (Moutinho 81); Bernardo Silva, Falcao (c, Raggi 89), Germain (Carrillo 77). Substitutes (not used): De Sanctis, Boschilia, Mbappe, Diallo.
Spurs: Lloris (c); Trippier, Dier, Wimmer, Rose; Wanyama, Dembele (Eriksen 64), Alli, Winks (Sissoko 74), Son (Janssen 64); Kane. Substitutes (not used): Vorm, Walker, Vertonghen, Nkoudou.
Goals: Monaco – Sidibe 48, Lemar 52; Spurs – Kane 51 (pen).
Yellow cards: Monaco – Glik 51, Falcao 57; Spurs - Dier 11, Dembele 21, Trippier 84.
Referee: Bjorn Kuipers.
We’ve another London derby in the Premier League on Saturday as we visit Chelsea. The Blues are the in-form side in the division having won all of their last six games, a run that has seen them climb to top spot in the table.