More than 85,000 packed the national stadium -- Tottenham's adopted home for this year's Champions League -- on a balmy Riviera-like night in London but the club's second campaign among Europe's elite began in disheartening fashion.
Toby Alderweireld's header shortly before the interval offered hope of a second-half siege but Monaco, leaders of Ligue 1, held out comfortably to top the early group standings.
"We conceded a goal after 16 minutes that, at this level and in football, you cannot concede," Spurs boss Mauricio Pochettino said. "We improved in the second half and had chances to win.
"They had only two shots on target and scored twice. We feel very disappointed with the result, we deserved more but you cannot concede like we did."
The crowd, beating the 75,038 that watched Tottenham play Sunderland at White Hart Lane in 1938, was a new record for a home fixture for a British club in the competition.
And they pumped up the volume as the game kicked off with Spurs on the front foot and Son Heung-Min close to giving the hosts a dream start with a shot cleared off the line.
Near silence descended on the huge stadium when Monaco, who stunned Arsenal two seasons ago in the last 16, took the lead with their first real incursion after 15 minutes.
Argentine playmaker Erik Lamela carelessly gave the ball away in his own half and Portugal international Silva ran on unopposed before smashing a shot past Hugo Lloris.
Mauricio Pochettino's Tottenham, known for their high-tempo football last season when they challenged for the Premier League title, struggled to exert any sustained pressure.
Monaco looked comfortable and doubled their lead in the 31st minute when Djibril Sidibe slung in a hopeful cross and it rebounded off the body of Spurs left back Ben Davies to Lemar, on for the injured Nabil Dirar, to send a powerful shot into the roof of the net past Lloris.
The tiny travelling pod of Monaco fans numbering no more than 350 celebrated but it was the vast home majority who found their voices again just before halftime when Lamela's corner was headed powerfully home by Belgian Alderweireld.
Dele Alli was desperately close to equalising in first-half stoppage time, stretching to reach a Lamela cross.
Tottenham were re-energised at the start of the second half and Alli brought a superb save from Danijel Subasic after letting fly with a dipping volley from 25 metres.
Harry Kane then found himself clear on goal but delayed his shot far too long and was closed down.
Kane wasted an even better chance with 12 minutes remaining, shooting straight at Subasic from in front of goal.
Monaco were calm thereafter and suffered no late alarms.
(Reporting by Martyn Herman; Editing by Toby Davis)
