Question:  when was the Swiss professional tennis player. was the defending champion in the 2017 US Open – Men's Singles born
Context: The 2012 US Open Men's Singles final was the championship tennis match of the Men's Singles tournament at the 2012 US Open.  In the final, Andy Murray defeated defending champion Novak Djokovic 7–6, 7–5, 2–6, 3–6, 6–2 to win the match.  It was the equal-longest US Open men's final in history, lasting 4 hours and 54 minutes (equalling the 1988 US Open final played by Ivan Lendl and Mats Wilander), and the equal second-longest men's final in the Open era, only behind the 2012 Australian Open final.  By winning the 2012 US Open, Murray became the first British man since Fred Perry in 1936 to win a Grand Slam singles title, and the first British man in the Open Era to do so.  The match is a significant part of the rivalry between the two players.  This match also marked a milestone for Murray, as it was his 100th match win at a grand slam tournament. Jamie Murray is a professional tennis player who is the current British number one doubles player.  He has reached eight grand slam finals in total: (4 Doubles, 4 Mixed), he has won the mixed doubles at the 2007 Wimbledon Championships, 2017 Wimbledon Championships and 2017 US Open, and the men's doubles at the 2016 Australian Open and 2016 US Open, and has finished as runner-up in the men's doubles tournament at the 2015 Wimbledon Championships and 2015 US Open and in mixed doubles at the 2008 US Open.  Murray has been ranked as high as World No. 1 in the ATP doubles rankings, and was the first Britain to be ranked as world number one since the introduction of computerised world rankings in the 1970s.  He is currently ranked at world No. 5. Juan Martín del Potro (] , born 23 September 1988), also known as Delpo is an Argentinian professional tennis player who is currently ranked world No. 24 in men's singles by the Association of Tennis Professionals (ATP).  His biggest achievement has been winning the 2009 US Open, defeating Rafael Nadal in the semifinal and 5-time defending champion Roger Federer in the final.  He was the first to defeat both Federer and Nadal during the same major and was the only man outside the Big Four to win a major between the 2005 French Open and the 2013 US Open, a span of 35 tournaments.  He is also the second Argentine and the fifth-youngest man to win the US Open in the Open Era.  Other career highlights include winning the bronze medal in men's singles at the 2012 London Olympics and the silver medal at the 2016 Rio Olympics and being part of his country's successful Davis Cup team; but his career has also been hampered by a succession of wrist injuries. Stanislas Wawrinka (] ; born 28 March 1985) is a Swiss professional tennis player.  Professionally called "Stan", he reached a career-high Association of Tennis Professionals (ATP) world No. 3 singles ranking for the first time on 27 January 2014.  His career highlights include three Grand Slam titles at the 2014 Australian Open, 2015 French Open and 2016 US Open, where he defeated the world No. 1 player in the final on all three occasions, reaching the final of the 2017 French Open, winning an ATP World Tour Masters 1000 title at the Monte-Carlo Masters in 2014, and reaching three other finals at 2008 Rome, 2013 Madrid and 2017 Indian Wells.  He is sometimes considered as part of the newly established "Big Five", an expansion of the Big Four, which already consists of Roger Federer, Rafael Nadal, Novak Djokovic and Andy Murray. Marin Čilić (; born 28 September 1988) is a Croatian professional tennis player.  Over the course of his career, Čilić has won 17 ATP singles titles, including the 2014 US Open.  His career-high singles ranking is world No. 5, achieved in September 2017.  Čilić first came to international prominence by defeating then-World No. 2 Andy Murray in the fourth round of the 2009 US Open.  He followed this by reaching the semifinals of the 2010 Australian Open.  Among other achievements, Čilić was runner-up at the 2017 Wimbledon Championships, and was a semifinalist at the 2015 US Open as defending champion.  Čilić is currently the youngest active male player to have won a slam.  Čilić has reached at least the quarterfinal in all four grand slam tournaments.  He has a very powerful serve and very powerful groundstrokes. The 2017 BB&T Atlanta Open was a professional tennis tournament played on hard courts.  It was the 30th edition of the tournament, and part of the 2017 ATP World Tour and the 2017 US Open Series.  It took place at Atlantic Station in Atlanta, United States between July 24 and 30, 2017.  It was the first men's event of the 2017 US Open Series. This is a list of the main career statistics of Czech professional tennis player Petra Kvitová.  To date, Kvitová has won 20 singles titles including two Grand Slam singles titles at the Wimbledon Championships, one WTA Tour Championships singles title, two WTA Premier Mandatory singles titles and four WTA Premier 5 singles titles.  She was also the bronze medallist at the 2016 Rio Olympics, a semifinalist at the 2010 Wimbledon Championships, 2012 Australian Open and 2012 French Open and a quarterfinalist at the 2011 Australian Open, 2012 Wimbledon Championships, 2013 Wimbledon Championships, 2015 US Open and 2017 US Open.  Kvitová reached her career-high ranking of world no. 2 on 31 October 2011. Lucie Šafářová (] ; born 4 February 1987) is a Czech professional tennis player from Brno.  She is currently the WTA world No. 1 doubles player.  Šafářová has won seven WTA tour singles titles, fifteen doubles titles and reached the quarterfinals of the 2007 Australian Open by upsetting defending champion Amélie Mauresmo in the fourth round.  She reached her first Grand Slam semifinal at the 2014 Wimbledon Championships and her first Grand Slam final at the 2015 French Open.  She also won the 2015 Australian Open, 2015 French Open, 2016 US Open, 2017 Australian Open and 2017 French Open women's doubles titles partnering with Bethanie Mattek-Sands. This is a list of the main career statistics of Swiss professional tennis player, Stan Wawrinka.  To date, Wawrinka has won sixteen ATP singles titles, including three Grand Slam singles titles at the 2014 Australian Open, the 2015 French Open, and the 2016 US Open, and one ATP Masters 1000 title at the 2014 Monte-Carlo Rolex Masters.  He was also a semifinalist at the 2013 US Open, the 2015 Australian Open, the 2015 US Open, and the 2013, 2014 and 2015 ATP World Tour Finals.  He also has reached the quarterfinals at 2014 and 2015 Wimbledon.  Wawrinka also won a gold medal partnering Roger Federer in men's doubles for Switzerland in the 2008 Summer Olympics in Beijing, beating Swedish team Simon Aspelin and Thomas Johansson.  In 2014 Wawrinka was part of the Swiss National Team, winning the Davis Cup for the first time. Stan Wawrinka was the defending champion, but was unable to defend the title due to a knee injury that ended his season prematurely.  Wawrinka's withdrawal ended his streak of 50 consecutive grand slam appearances, dating back to the 2005 French Open.
Answer: 28 March 1985