The Greek three-time Monte Carlo champion fell 7-5, 6-4 to world No. 19 Cerundolo. Tsitsipas had led 5-3 in the opening set, but the 27-year-old Argentine won four consecutive games to take the lead.
In the second set, Tsitsipas recovered from 0-4 down to 4-4, only to lose his serve in the ninth game, allowing Cerundolo to seal the victory.
Prior to this year, Tsitsipas held a 22-4 record in Monte Carlo across seven appearances and had never lost in the first round. He won the tournament in 2021, 2022, and 2024, and had not exited before the quarter-finals since 2019.
Starting the tournament ranked 48th with 995 points, Tsitsipas lost 180 points from his quarter-final finish last year, resulting in a 16-place drop to world No. 64 in the live ATP Rankings.
This is the latest setback in a difficult period for the 27-year-old, who was ranked 30th in February before losing points from Dubai, Indian Wells, and Miami in 2025. Tsitsipas was world No. 8 at this stage last year when he competed in the 2025 Monte Carlo Masters.
