Thiago Monteiro upset third-seeded Dominic Thiem 6–1, 3–6, 7–6 in the first round of the ATP 250 Rio de Janeiro event on clay on 20 February 2023, claiming a significant result against the tournament favourite. Thiem, priced at 1.51 odds, entered as the clear pre-match favourite, but Monteiro capitalised on inconsistency from the Austrian, taking the opening set decisively before Thiem levelled in the second. The decider proved decisive, with Monteiro prevailing in the tiebreak to secure his passage. The result represents a notable upset for the home player and serves as a reminder of Thiem's ongoing struggles to regain form on the professional circuit.