Vincent Aboubakar scored the only goal as Lorient condemned Valenciennes to a third consecutive Ligue 1 defeat.
VA beat Toulouse 3-0 on the opening day of the season but they have not claimed a point since then and things got worse for them on Saturday night with the dismissal of Rudy Mater for two bookable offences.
For Lorient it was a second win of the season and moves them on to six points after their first four games.
The home side could have had the lead after five minutes as Alain Traore made a surging run down the left and crossed to find Raphael Guerreiro but he could only volley over the bar.
Just eight minutes later they were ahead as Yann Jouffre found Aboubakar in the box and the Camerooninan striker rounded Fabien Audard and slotted into the empty net.
The first half was one of few chances but Valenciennes could have been level five minutes before the break as Jean-Christophe Bahebeck unleashed a shot from 25 yards but his effort cleared the bar.
Nine minutes after the interval Mater found Maor Melikson on the edge of the area and his shot brought a superb save from Audard.
The visitors were pressing for an equaliser and Mater was nearly the man to provide it as his free kick brought another full-stretch save from Audard.
Gilles Sunu teed up Mathieu Coutadeur as Lorient pressed for a second but Nicolas Penneteau made a good block and Sunnu was the creator again two minutes later but this time Kevin Monnet-Paquet's shot was saved by Audard.
Mater was then sent off as his tackle on Sadio Diallo earned him a second yellow card four minutes from time.