Question: The Men's 2013 US Open Series was won by which Spanish player, currently World #1?
Sentence (from "2013 US Open Series"): Rafael Nadal and Serena Williams were the US Open Series winners, making them eligible for a $1 million bonus if either also won the US Open, a feat which they both accomplished, hence receiving the largest paychecks to date for a single tennis tournament, totalling $3.6 million each.
Relevant evidence: Yes