The Principality side were in first gear for much of the encounter but ground out a victory with just three minutes of the Ligue 1 match remaining, through a fantastic goal
Valenciennes may already have been relegated, but they almost scored after just 30 seconds when Aymen Abdennour misjudged the ball in the air and Abdul Majeed Waris forced a good block from Monaco ‘keeper Sergio Romero.
Ariel Jacobs, the Valenciennes coach, had demanded his side finished this sorry campaign in "an honourable fashion" and the host club went about this match in the proper manner, forcing several corners in the opening exchanges.
In reply, Valere Germain clipped the crossbar with a shot, but this game felt like an end of season affair, with time ticking away on the 13/14 season, and similarly, counting down on Claudio Ranieri’s time in chage of the Principality.
With Champions League football secure, Monaco looked disinterested at times and toiled to find any structure to their play.
However, five minutes from half-time, the visitors took the lead. Yannick Carrasco worked an opening for Germain, and the visiting captain tucked his shot past the onrushing Nicolas Penneteau.
Given how impressive Monaco have been away from home this season, second only to PSG with 35 points claimed, there was a feeling that this encounter could be over at half-time.
Valenciennes stopper Lindsay Rose – who is expected to leave the club this summer - was booked early in the second period for one robust challenge too many.
The game lacked any sense of urgency, but on 70 minutes and out of nothing, Valenciennes produced an equaliser. Maor Melikson worked his way in from the left, his cut back flat-footing the third best defence in Ligue 1, enabling Tongo Hamed Doumbia to side foot a shot past Romero.
Within a minute, Carl Medjani - against his parent club - came close with a shot and Monaco, having looked unperturbed, suddenly appeared rattled.
Their defending became desperate at times as Abdennour and Uwa Elderson Echiejile were yellow carded in quick succession.
Abdennour’s abysmal evening continued when his slip left Waris in the clear, but he fired wildly over when a winner looked on.
It proved a costly miss for the hosts, as three minutes from time Nabil Dirar ran at the Valenciennes back line, before cutting in on his left foot and firing a long distance drive high past the stationary Penneteau.