Question: The Men's 2013 US Open Series was won by which Spanish player, currently World #1?

Context articles: 2013 US Open Series
2014 US Open Series
2011 US Open Series
2017 US Open Series
2012 US Open Series
2015 US Open Series
2013 Winston-Salem Open
Rafael Nadal
2013 New Haven Open at Yale
2016 US Open Series

In tennis, the 2013 US Open Series (known as Emirates Airline US Open Series for sponsorships reasons) was the tenth edition of the US Open Series, which included ten hard court tournaments that started on July 20, 2013 in Atlanta and concluded in Winston-Salem for the men and in New Haven for the women on August 24, 2013.
 This edition consisted of four separate men's tournaments and four women's tournaments, with the Western & Southern Open hosting both a men's and women's event.
 The series was headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.
 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.
In tennis, the 2014 US Open Series (known as Emirates Airline US Open Series for sponsorship reasons) was the eleventh edition of the US Open Series, which included nine hard court tournaments that started on July 21, 2014 in Atlanta and concluded in Winston-Salem for the men and in New Haven for the women on August 23, 2014.
 This edition consisted of four separate men's tournaments and three women's tournaments, with the Western & Southern Open hosting both a men's and women's event.
 The series was headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.
 Milos Raonic and Serena Williams were the US Open Series champions in 2014.
 Serena Williams improved the biggest payout in professional tennis history record which she previously shared with Rafael Nadal.
 The new record was then set at $4 million.
In tennis, the eighth edition of the US Open Series (known as Olympus US Open Series for sponsorships reasons), includes ten hard court tournaments that start on July 18, 2011 in Atlanta and will end in Winston-Salem for the men and in New Haven for the women on August 28, 2011.
 This edition has scheduled five separate men's tournaments, four women's tournaments, and the Western & Southern Open that will host both a men's and women's event.
 The series includes two ATP World Tour Masters 1000 and two WTA Premier 5 events to headline the series.
In tennis, the 2017 US Open Series was the fourteenth edition of the US Open Series, which comprised a group of hard court tournaments that started on July 24, 2017 in Atlanta and concluded in Connecticut for the women and in Winston-Salem for the men on August 26, 2017.
 This edition consisted of three separate men's tournaments and three women's tournaments, with the Western & Southern Open hosting both a men's and women's event.
 The series was headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.
In tennis, the ninth edition of the US Open Series (known as Emirates Airline US Open Series for sponsorships reasons), included twelve hard court tournaments that started on July 9, 2012 in Stanford and concluded in Winston-Salem for the men and in New Haven for the women on August 26, 2012.
 This edition scheduled four separate men's tournaments and four women's tournaments – the Citi Open and the Western & Southern Open hosted both a men's and women's event.
 The series was headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.
 The series winners were Novak Djokovic and Petra Kvitová.
In tennis, the 2015 US Open Series (known as Emirates Airline US Open Series for sponsorship reasons) is the twelfth edition of the US Open Series, which includes a group of hard court tournaments that starts on July 27, 2015 in Atlanta and concluded in Winston-Salem for the men and in New Haven for the women on August 30, 2015.
 This edition consists of three separate men's tournaments and three women's tournaments, with the Western & Southern Open hosting both a men's and women's event.
 The series is headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.
The 2013 Winston–Salem Open was a men's tennis tournament played on outdoor hard courts.
 It was the 45th edition of the Winston-Salem Open (as successor to previous tournaments in New Haven and Long Island), and was part of the ATP World Tour 250 Series of the 2013 ATP World Tour.
 It took place at the Wake Forest University in Winston-Salem, North Carolina, United States, from August 18 through August 24, 2013.
 It was the last event on the 2013 US Open Series before the 2013 US Open.
Rafael "Rafa" Nadal Parera (] , ] ; born 3 June 1986) is a Spanish professional tennis player, currently ranked World No. 1 in men's singles.
 Known as "The King of Clay", he is widely regarded as the greatest clay-court player in history.
 His evolution into an all-court threat has established him as one of the greatest tennis players ever.
The 2013 New Haven Open at Yale (New Haven Open at Yale presented by First Niagara "for sponsorship reasons") was a tennis tournament played on outdoor hard courts.
 It was the 45th edition of the New Haven Open at Yale, and part of the Premier Series of the 2013 WTA Tour.
 It took place at the Cullman-Heyman Tennis Center in New Haven, Connecticut, United States, from August 16 through August 24.
 It was the last event on the 2013 US Open Series before the 2013 US Open.
In tennis, the 2016 US Open Series (known as Emirates Airline US Open Series for sponsorship reasons) is the thirteenth edition of the US Open Series, which includes a group of hard court tournaments that starts on July 18, 2016 in Stanford and concludes in Connecticut for the women and in Winston Salem for the men on August 27, 2016.
 This edition consists of three separate men's tournaments and three women's tournaments, with the Western & Southern Open hosting both a men's and women's event.
 The series is headlined by two ATP World Tour Masters 1000 and two WTA Premier 5 events.