Joseph Akpala was on target as Oostende clinched a Europa League qualification ticket despite a 3-2 defeat to champions, Anderlecht on Sunday.
Antonio Milic got Yves Vanderhaeghe's men in front in the 28th minute but David Rozehnal scored an own goal to gift the home side a leveler three minutes from half time.
In the second half, Leander Dendoncker put Rene Weiler's side ahead in the 64th minute but the Nigerian forward leveled matters four minutes later.
However, it was Frank Acheampong's 78th minute goal that ensured the Brussel based outfit sealed their 34th Jupiler Pro League title at the Constant Vanden Stock Stadium.
Despite the defeat, De Kustobys finished fourth in the six-team Championship play-off log with 37 points as the former Werder Bremem forward got his third goal in 17 games.