Question: Which tennis player won a major tennis championship in singles, Juan Martín del Potro or Bob Bryan?
Sentence (from "Michaël Llodra"): He is a successful doubles player with three Grand Slam championships and an Olympic silver medal, and has also had success in singles, winning five career titles and gaining victories over Novak Djokovic, Juan Martín del Potro, Tomáš Berdych, Robin Söderling, Jo-Wilfried Tsonga, Nikolay Davydenko, Janko Tipsarević and John Isner.
Relevant evidence: No