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Berbatov could have fired his side in front when he latched on to a cross into the box, but from close range and a tight angle, the striker was unable to find a way through Riou.
Monaco were testing the defensive capabilities of the visitors and Joao Moutinho almost broke the deadlock as he picked the ball up on the edge of the area and fired a low drive towards the bottom corner, but Riou turned his strike past the post.
The home side were dealt a huge blow in the 34th minute when Wallace was sent off for a high boot on Benjamin Bourigeaud in a 50-50 challenge, but the referee deemed that the tackle from the defender was dangerous.
In the second half, Monaco had a chance to threaten when Tiemoue Bakayoko had space to run into down the right. The winger had Berbatov to hit in the box with only one defender to beat, but he put too much on his cross and the opening was spurned.
The hosts came within inches of going ahead in the 57th minute as Aymen Abedennour raided forward from the back and linked up with Berbatov. The defender struck an effort on the half-volley that Riou got a fingertip to and as a result the ball just bounced onto the bar and went over.
Monaco did take the lead in the 64th minute when Berbatov was held back in the area by Jerome Le Moigne and a penalty was awarded. The striker took the spot kick himself and calmly slotted the ball into the bottom corner.
The visitors pressed late in the game as Monaco failed to capitalise on half-chances that came their way, and Alharbi El Jadeyaoui drilled a left-footed volley that seemed destined for the top corner, but Subasic managed to parry the ball wide.
Monaco sealed their win in stoppage time when Ferreira Carrasco won the ball down the left and beat his man with skill, and then drilled an effort from distance past Riou.