Abstract text: Zymoseptoria tritici is a highly damaging wheat pathogen that colonizes exclusively the apoplast. To interfere with plant cell walls (PCWs) Z. tritici secretes cell wall-modifying enzymes (CWMEs), which presumably facilitate fungal invasion. However, CWMEs also lead to the release of cell wall-derived oligosaccharides that might trigger a defence response. Thus, plant pathogens need to coordinate and tightly control the release of CWMEs. In this work, we identified and characterized two CWMEs critical for pathogenesis by integrating transcriptomic, genetic and biochemical analyses. Two mannan-degrading enzymes, Ztman5 (endo-β-mannanase) and Ztman2 (exo-β-mannanase), are synchronously induced at the onset of the necrotrophic phase. ZtMan5 is the primary fungal enzyme responsible for mannan depolymerization. Its activity releases mannan-derived oligosaccharides (MOS), which act as elicitors of host immunity. Accordingly, infection assays using disruption mutants demonstrated that ZtMan5 is a negative regulator of virulence. To counteract this immune response, Z. tritici co-expresses ZtMan2, which depolymerizes MOS, thereby neutralizing their elicitor activity. We suggest that the coordinated action of both enzymes enables mannan breakage and the prevention of host recognition. This dual-enzyme strategy represents a critical adaptation of the pathogen to remodel PCWs.