A rotary mower cutting deck has a rear discharge opening across a rear end thereof and a center blade and a first side blade rotating in one direction and a second side blade counter-rotating in the opposite direction. A front flow control baffle has a first, rearwardly facing V-shaped apex located between the unidirectional blades and a second, rearwardly facing V-shaped apex between the center blade and the counter-rotating side blade. A first V-shaped flow deflector is mounted to the first apex with the first flow deflector pointing 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 is mounted to the second apex with the second flow deflector pointing upwardly to disrupt the convergence of the air flows from the center and second side blades.
