The defense that got Tottenham to the Champions League is what let them down

Harry Kane, Dele Alli or any of Tottenham Hotspur's other youngsters might have been the talk of the Premier League last season if it wasn't for Leicester City's miraculous title. A bunch of young English players starring as a London club makes the jump to the top three and a Champions League place is a great story, and it did get play. Until the team's late-season swoon, Spurs' group of brilliant attackers were darlings. But it wasn't them who made for the backbone of Spurs' terrific team — it was the defense.

And yet on Wednesday, in their first match back in the Champions League, their defense is what cost them three points. That back line handed Monaco a 2-1 win.

Erik Lamela set Monaco's first goal in action by bizarrely taking the ball off Eric Dier's foot then giving it away in a poor position. But from there, Ben Davies defended the counterattack terribly and let Bernardo Silva get a full head of steam. Then Jan Vertonghen, in a 1v1 situation, retreated far too quickly and gave way too much space to Silva, who hit a great shot. Lamela should have never put the defense in that situation, but they didn't handle it well at all and Spurs found themselves behind 15 minutes into a match they had otherwise dominated.

Mistakes aren't necessarily shocking in any match, especially at the back. After all, if it were easy then there wouldn't be any goals. But these were ordinary plays and this is no ordinary back line. No team gave up fewer goals than Spurs' last season. They were impenetrable, and while Toby Alderweireld once again looked like the best defender in England on this day — flawless in defense and even adding a goal on a corner kick — the rest weren't up to the task.

This all came on a night when Spurs were better than Monaco anyway. It wasn't like they were a disaster, and a couple bad moments in 90 minutes are to be expected. Mauricio Pochettino will probably be happy about most of what he saw.

Still, Spurs' return to the Champions League was ruined by their defense. Their defense that put them in the Champions League. Their defense that nobody in the Premier League was better than a year ago. And it happened at home against a team they expect to compete with for a top-two spot in their group. That's going to be a tough one to take.

MORE FROM FOX SOCCER