Photocatalytic ozonation (PH-OZ) process using TiO2 photocatalyst conducted in acidic water environment often leads to a synergistic effect in terms of decomposition and mineralisation of aqueous organic contaminants. The synergism is greatly influenced by photocatalyst physicochemical properties and pollutant type, besides pH, temperature, O3 concentration and other factors. Herein, five different commercial TiO2 photocatalysts (P25, PC500, PC100, PC10 and JRC-TiO-6) were used in photocatalysis (O2/TiO2/UV), catalytic ozonation (O3/TiO2) and PH-OZ (O3/TiO2/UV) advanced oxidation systems for degradation of two pollutants (dichloroacetic acid - DCAA and thiacloprid), simultaneously present in water. Synergistic effect in PH-OZ was much more expressed in the case of thiacloprid which did not significantly adsorb on the photocatalyst surface—in contrast to DCAA with stronger adsorption. Faster PH-OZ kinetics correlated to the higher exposed surface of TiO2 agglomerates, regardless of (lower) BET surfaces of primary particles. But, DCAA mineralisation reactions on a TiO2 surface were much faster in comparison to thiacloprid degradation reactions in solution bulk. Hence, we propose that high BET surface area of the photocatalyst is crucial for fast surface reactions (DCAA mineralisation), while good dispersity—high exposed surface of aggregates—and charge separation play a major role when it comes to photocatalytic degradation or PH-OZ of less-adsorbed organic pollutants (thiacloprid).