Lucas Ocampos' tap-in guided Monaco to a 1-0 Champions League victory at Bayer Leverkusen to ensure Group C is wide open.
The Argentine winger latched onto Nabil Dirar's cross to cap a fine counter-attack that allowed Monaco to frustrate the hosts, who dominated territory and possession.
Leverkusen could have sealed top spot and their first-ever seeding for the Champions League round of 16 with victory over their stuttering French visitors.
Monaco arrived in Germany without a win in four matches, but quickly set about denying the hosts safe passage to the next round.
Ocampos' winning goal leaves Leverkusen top of the Group C standings on nine points, but Monaco now only trail by one: so either side can still top the pool with one round of fixtures remaining.
Monaco host Zenit on Tuesday, December 9, with Leverkusen travelling to Benfica, with the matches now effectively a shoot-out for top spot.
Monaco boss Leonardo Jardim's plan to frustrate Leverkusen into a mistake worked perfectly, with the possession-hogging hosts unable to convert their control.
Monaco's victory also dumped Group C's bottom side Benfica out of European competition altogether for the campaign, after the Portuguese club lost out 1-0 at Zenit St Petersburg in Wednesday's early kick-off.
Lars Bender blasted against the bar for Leverkusen after 26 minutes in the only real chance of a tetchy first-half, the teams turning round in stalemate with the hosts by far the more frustrated.
Germany's 19-cap holding midfielder left Monaco stopper Danijel Subasic dumbfounded as his effort rebounded off the frame of his goal, but that chance aside the opening exchanges proved hugely frustrating for the home side.
Monaco had clearly pitched up with the intention of squeezing their hosts through a regimented rearguard effort.
Leverkusen dominated territory and possession in that first-half, but failed to capitalise and match that control with clear-cut scoring chances.
Aymen Abdennour and Ricardo Carvalho marshalled not only Monaco's central defence but also the visitors' entire framework, halting Leverkusen at all but every turn.
The second-half continued in much the same vein as the first, but as time ticked by Monaco gained increasing confidence.
All that patience and diligence came to fruition then, when the visitors broke on the counter and Dirar found Ocampos in the 72nd minute who turned in and sparked jubilant French celebrations.