This work focused on the degradability of Pythium debaryanum cell wall by cellulase enzymes produced by Bacillus subtilis MK537378 and Trichoderma reesei MK934489. B. subtilis showed higher Exo-1,4-β-D glucanase and Endo-1,4-β D-glucanase activities than T. reesei while the highest β-glucosidase activities were recorded for T. reesei. Antagonistic activities against P. debaryanum were investigated by the tested B. subtilis and T. reesei. Moreover, the cellulolytic activity of both B. subtilis and T. reesei against P. debaryanum was confirmed by using Congo red staining technique. Microscopic observations showed clear hyphal lysis and degradation of the fungal cell wall in a dual plate assay. Results of the greenhouse experiment emphasized that the inoculated tomato seeds with B. subtilis or T. reesei in the presence of P. debaryanum showed 73.5% and 76% reduction in disease incidence, respectively as compared to the seed treated with pathogen alone (85%). Dehydrogenase activity (DHA) of soil rhizosphere was significantly increased in all inoculated soil with B. subtilis and/or T. reesei compared with uninoculated ones. The inoculation of tomato with B. subtilis and T. reesei in presence of P. debaryanum induced high activities of peroxidase, polyphenoloxidase, and chitinase by increasing 49.3, 55.2, and 56.9%, respectively, over the control. The growth parameters and yield of the tomato plants significantly increased in response to the inoculation of B. subtilis MK537378 and T. reesei MK934489 compared to individual inoculation.