Tomi Horvat produced a sensational strike to put the hosts in front and even when Harry Kane brought Spurs level, Amadej Marosa netted a 94th minute winner to leave Antonio Conte's side's future in the Conference League in the balance.
In Spurs' last game, they came from behind to secure a morale boosting win against Leeds United which gave Antonio Conte his first Premier League win.
Against the Slovenian outfit though, they did not carry any of that confidence over and even with Kane bringing Spurs level, they were lacklustre throughout.
A slow start was duly punished as Conte's side went 1-0 down early on which brought out a damming statement from Bent on Sanchez's role in the goal.
"Great goal, Davinson Sanchez's defending was awful," Bent said on talkSPORT Drive.
Despite Kane's equaliser, it was a disappointing evening for most of the Spurs players and a missed chance to impress Conte.
Matt Doherty made a rare appearance, while Dele Alli, Tanguay Ndombele and Ryan Sessegnon also featured.
Unfortunately for all four players they were unable to make the most of the opportunity.
Doherty and Alli were both subbed before the hour mark, Ndombele with 15 minutes to go and Sessegnon was sent off in the first half for two bookable offences.
As the game was dwindling out for a draw, the hosts counter-attacked looking for the winner.
Ben Davies slipped in midfield and as the ball was moved forward quickly with seconds to spare, Marosa ran at Sanchez.
Clearly not learning from his first goal, the Colombian centre-back allowed the attacker to cut inside again and despite his best efforts, the ball deflected off him to bounce over goalkeeper Pierluigi Gollini and in doing so, inflicted an embarrassing loss for Conte.
Fortunately for the Lilywhites, they are still firmly in contention to progress and have qualification in their own hands, but are up against Rennes who have won the group and are certain not to make things easy for the Premier League side.
Spurs should have had enough quality to come away with three points from Slovenia but leave the country empty handed.
Now they need to dust themselves off quickly and hope to get back to winning ways in the league as they travel to 18th placed Burnley.