Abiotic stress adversely affects crop production, causing yield reductions in important crops, including tomato (Solanum lycopersicum). Among different abiotic stresses, drought is considered to be the most critical one since limited water availability negatively impacts plants growth and development, especially in arid or semi-arid areas. The aim of this study was to understand how biostimulants may interact with critical physiological response mechanisms in tomato under limited water availability and to define strategies to improve tomato performances under drought stress. We investigated physiological responses of the tomato genotype E42 grown in open field under control condition (100% irrigation) and limited water availability (50% irrigation) and treated or not with a novel plant-based biostimulant named CycoFlow (Agriges). Under limited water availability plants treated with the biostimulant showed a reduction in osmotic pressure (-22.50% vs non treated plants). The biostimulant treatment enhanced plant growth (biomass) under control (+ 99.02% vs non treated plants) and stress conditions (+296.63% vs non treated plants). Also, biostimulant treated plants had higher pollen viability (+ 50.94% vs non treated plants) and higher yield per plant (+ 563.90% vs non treated plants) under limited water availability. The treatment with the biostimulant had also an effect on antioxidants and pigments content, both in leaves and fruits. In particular, the content of phenols increased under limited water availability (+ 11.83% vs non treated plants), while the ascorbic acid content decreased (- 7.33% non treated plants). Altogether, these results indicate that the application of the biostimulant CycoFlow to tomato plants improved plant performances under limited water availability.