Question: At 2006 Dubai Tennis Championships – Men's Singles, Rafael Nadal defeated the defending champion who has won how many Grand Slam singles titles?
Context: Roger Federer reached all four Grand Slam finals in 2006, winning three of them.  His only Grand Slam loss came against Rafael Nadal in the French Open final in four sets, 6–1, 1–6, 4–6, 6–7(4).  This was the first time they had met in a Major final.  In the other three Grand Slams of 2006, Federer defeated Nadal in the final of the Wimbledon Championships, 6–0, 7–6(5), 6–7(2), 6–3.  He defeated Marcos Baghdatis, 5–7, 7–5, 6–0, 6–2, at the Australian Open and Andy Roddick, 6–2, 4–6, 7–5, 6–1, at the US Open.  In addition, Federer made it to six ATP Masters Series 1000 finals, winning four on hard surfaces and losing two on clay to Nadal.  Also, Federer won one ATP 500 series event in Tokyo, three ATP 250 series events in Doha, Halle, and Basel, and captured the Year-End Championships for the third time in his career.  In December 2011, Stephen Tignor, chief editorial writer for Tennis.com, ranked Federer's 2006 season as the second greatest season of all-time during the open era; behind only Rod Laver's Calendar Grand Slam year of 1969. Roger Federer (] ; born 8 August 1981) is a Swiss professional tennis player who is currently ranked world No. 2 in men's singles tennis by the Association of Tennis Professionals (ATP).  Federer has won 19 Grand Slam singles titles, the most in history for a male tennis player and has held the world No. 1 spot in the ATP rankings for a record total of 302 weeks, including a record 237 consecutive weeks.  After turning professional in 1998, he was continuously ranked in the top ten from October 2002 to November 2016. Novak Djokovic was the defending champion and successfully defended his title against Rafael Nadal in the final.  The final took 5 hours and 53 minutes to complete, which was the longest match in Australian Open history and the longest Grand Slam singles final in the Open Era.  This match marked Nadal's third consecutive grand slam final loss against Djokovic and thus he went on to become the first and thus far only player to lose three Grand Slam finals in a row in the Open Era. The 2017 Australian Open Men's Singles final was the championship tennis match of the Men's Singles tournament at the 2017 Australian Open.  It was contested between Roger Federer and Rafael Nadal, ranked 17th and 9th in the world respectively.  It was their record ninth meeting in a Grand Slam final in their rivalry, and their 1st meeting in a Grand Slam final since the 2011 French Open.  In a rematch of the 2009 Australian Open final, which Nadal won in 5 sets, Roger Federer won the duel in 5 sets, beating Nadal for the first time in a Grand Slam since the 2007 Wimbledon final.  He also trailed Nadal 3–1 in the final set but won 5 games in a row to win the title.  This ended a 6-match losing streak against Nadal in Grand Slam events.  Having lost all of their previous three encounters, this was the first time Federer defeated Nadal at the Australian Open and also marked Federer's first Grand Slam victory over Nadal outside the grass courts of Wimbledon.  Federer extended his record of Grand Slam men's singles titles to 18, marking the third time he broke his own all-time record, after breaking the previous record of 14, held by Pete Sampras. Roger Federer won two Majors in 2009, the French Open, defeating Robin Söderling in the final, and the Wimbledon Championships with a victory over Andy Roddick.  In addition, Federer made two other Grand Slam finals, Australian Open losing to Rafael Nadal, and the US Open, losing to Juan Martín del Potro.  Federer went on to win two other Master Series 1000 tournaments: in Madrid over Rafael Nadal, and in Cincinnati over Novak Djokovic.  He lost in one 500 level event final in Basel to Djokovic.  During the year, Federer completed the Career Grand Slam by winning his first French Open title, and won a record fifteenth Grand Slam singles title, one more than Pete Sampras' mark of fourteen. The Dubai Tennis Championships (also known as the Dubai Duty Free Tennis Championships for sponsorship reasons) (formerly known for sponsorship reasons as the Barclays Dubai Tennis Championships and the Dubai Duty Free Men's and Women's Championships) is a professional tennis tournament owned and organized by Dubai Duty Free and held annually in Dubai, United Arab Emirates on outdoor hardcourts.  The courts usually have a medium-fast speed considered to be similar in speed to the Shanghai and Swiss Indoor (Basel) courts, all of which are usually somewhat slower than the Cincinnati Master's Courts.  The tournament takes place at the end of February and organizes a men's and women's event.  The tournament takes place under the patronage of Sheikh Mohammed bin Rashid Al Maktoum, Vice-President and Prime Minister of the UAE and ruler of Dubai.  In 2001 the ATP upgraded the tournament from a 250 level to a more prestigious 500 level tournament.  Prior to the 1990s there was an annual Dubai Tennis Championship played at the British Embassy. The 2012 French Open Men's Singles final was the championship tennis match of the Men's Singles tournament at the 2012 French Open.  In the final, Rafael Nadal defeated Novak Djokovic 6–4, 6–3, 2–6, 7–5 to win the match.  It was a Major final match of historic proportions, as Rafael Nadal was looking to become the first man to win seven French Open titles, thus breaking the record previously held by Björn Borg, who won six titles, and equalling the record held by Chris Evert, who won seven titles, whilst Novak Djokovic was looking to become the first man since Rod Laver in 1969 to hold each of the four Major titles simultaneously.  As well, Djokovic had defeated Nadal in the previous 3 Grand Slam finals and Nadal was trying to avoid coming runner-up in all 4 tournaments to the same player. Roger Federer was the defending champion but lost to Rafael Nadal in the final, 2–6, 6–4, 6–4. Li Na (; ; born 26 February 1982) is a retired Chinese professional tennis player, who achieved a career-high WTA-ranking of world No. 2 on 17 February 2014.  Over the course of her career, Li won seven WTA singles titles and two Grand Slam singles titles at the 2011 French Open and 2014 Australian Open.  Li's rise to prominence came after those victories, which made her the first and only Grand Slam singles champion from East Asia and Asia as a whole.  Prior to this, she had already become the first player representing an East Asian and Asian country to appear in a Grand Slam singles final, a milestone she achieved at the 2011 Australian Open.  Li was also the runner-up at the 2013 Australian Open and 2013 WTA Tour Championships, a three-time quarterfinalist at Wimbledon and a semifinalist at the 2008 Beijing Olympic Games and 2013 US Open.  Among her other most notable accolades, she was the first Chinese player to win a WTA tour title at the Guangzhou International Women's Open in 2004, the first to reach a Grand Slam singles quarterfinal at the 2006 Wimbledon Championships, and the first to break into the world's top 10.  Her feats have sparked a major population growth of tennis players in East Asia, earning her the reputation as the region's tennis pioneer and trailblazer. In the 2008 Wimbledon Championships Men's Singles Final, Rafael Nadal defeated five-time defending Wimbledon champion, Roger Federer in five sets to win his first Wimbledon title and fifth Grand Slam championship.  It was the longest championship match in Wimbledon history with play lasting four hours and 48 minutes, and with two rain delays.  The event stretched over seven hours ending just before nightfall, and is widely considered to be the greatest match in tennis history.
Answer: 19