A rotary mower cutting deck has a downwardly opening space and rear discharge opening. A center blade and a first side blade rotating in one direction and a second counter-rotating side blade are within the space. A front flow control baffle has a first V-shaped apex located between the unidirectional blades and a second V-shaped apex between the center blade and the counter-rotating side blade. A first V-shaped flow deflector mounted to the first apex points downwardly to cause many grass clippings from the first side blade to be directed to the rear discharge opening without passing to the center blade. A second V-shaped flow deflector mounted to the second apex points upwardly to disrupt the convergence of the air flows and clipping streams from the center and second side blades to maintain the quality of cut and reduce blow out.