Tottenham 1 Monaco 2
Tottenham's Champions League campaign began in disappointment as an English club-record home crowd watched them beaten 2-1 by Monaco at Wembley.
Spurs were given a harsh lesson in the ruthlessness of European football as goals from Bernardo Silva and Thomas Lemar were enough to give the French side an opening victory in Group E.
Toby Alderweireld's header had given Mauricio Pochettino's side hope on the stroke of half-time but while Tottenham had chances to snatch a point, Monaco held firm for a surprise win.
Spurs will play all their Champions League home games at Wembley this season while work on their new stadium continues and the 85,011 crowd was the largest home attendance in English club history, beating the 84,467 that witnessed Manchester City play Stoke in the FA Cup in 1934.
Any concerns about the atmosphere in an unfamiliar setting were quickly dismissed as Spurs came out to a sea of white shirts, roaring them on in what was their first outing at Europe's top table since 2011.
The little touches were there - the traditional video montage on the big screen before kick-off, the club motto ringed the stands and even the physio room donned pictures of successes past - but on the pitch, Pochettino's side failed to deliver.
Monaco sit top of Ligue 1 after taking 10 points from their opening four matches of the season and the visitors showed the sort of slick, tactical display Spurs will have to get used to if they want to progress out of the group.
The hosts started brightly and should have taken the lead when Harry Kane's cross found Son Heung-min unmarked at the back post but while the South Korean's finish beat goalkeeper Danijel Subasic, right-back Andrea Raggi scrambled across and made a last-ditch block.
Kane was causing Monaco problems down the right channel and soon after he was in again, spinning Jemerson to race clear but neither Erik Lamela nor Dele Alli were able to find a clean shot off the pull-back.
Monaco had ridden their luck early on but they survived and then stunned Spurs twice on the counter-attack.
Lamela was at fault for the first, giving away possession in midfield and as the ball fell to Silva he ghosted forward before driving into Hugo Lloris' far right-hand corner.
It was a goal out of the blue for the visitors but in the 31st minute they doubled their advantage, Djibril Sidibe's cross leaving Jan Vertonghen and Ben Davies in a tangle and then landing perfectly for Lemar to hammer home from close range.
The goals silenced the crowd and killed Tottenham's momentum but just as the visitors looked to have control, Alderweireld rose high and powered in Lamela's corner on the stroke of half-time.
Spurs jogged in to a hopeful roar from the crowd but Pochettino remained still with his arms folded and when the players emerged for the second half the Argentinian had replaced Son with Mousa Dembele, pushing Alli into a more offensive position behind Kane.
Alli's impact was swift as his dipping volley from 25 yards drew a leaping save from Subasic before the 20-year-old was wrestled to the ground by Fabinho at a corner.
Referee Gianluca Rocchi handed Fabinho a yellow card and for a moment appeared to have given a penalty when the Monaco players swarmed around in disbelief, only for order to be restored and the corner re-taken.
Spurs had chances late on, most notably when substitute Vincent Janssen held off Jemerson and then teed up Kane but the England striker was thwarted again as he fired straight at the goalkeeper.
A night that had began with a deafening roar ended in muted applause when the final whistle blew.