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Ríos holds the record for the most ATP Masters 1000 titles won on clay, with five triumphs. He achieved this feat by winning the Rome Masters in 1998, 2000, and 2002, the Hamburg Masters in 1999, and the Monte Carlo Masters in 2003. Ríos' dominance on clay was a testament to his exceptional footwork, powerful groundstrokes, and ability to adapt to the surface's unique challenges.