Question: In the 2015 Australian Open, the defending champion had reached a career high ranking of what?
Context: This list summarizes the main career statistics of Czech professional tennis player Lucie Šafářová.  To date, Šafářová has won seven WTA singles titles and fifteen WTA doubles titles including five Grand Slam doubles titles with Bethanie Mattek-Sands at the 2015 Australian Open and French Open,; the 2016 US Open and 2017 Australian Open and French Open.  Other highlights of Šafářová's career thus far include winning the 2015 Qatar Total Open, reaching the final of the 2015 French Open and making quarterfinal and semifinal appearances at the 2007 Australian Open and 2014 Wimbledon Championships, respectively.  Šafářová achieved career high singles and doubles rankings of World No. 5 and World No. 2 on 14 September 2015 and 30 January 2017. Rohan Bopanna (born 4 March 1980) is an Indian professional tennis player.  His singles career high ranking was World No. 213 in 2007 and his career high ranking in doubles was World No. 3 on 22 July 2013.  Recently, most of his appearances in professional tournaments have been in doubles matches.  He is a member of the Indian Davis Cup team since 2002.  In 2010, he finished as a runner-up in doubles at the US Open, partnering with Aisam-ul-Haq Qureshi.  He won the 2017 French Open - Mixed Doubles title with Gabriela Dabrowski of Canada becoming the fourth Indian player to win a Grand Slam title. Bernard Tomic (Croatian: "Tomić" ; born 21 October 1992) is an Australian professional tennis player who has a career high ranking of 17.  As a junior, Tomic enjoyed a successful career in which he won three Orange Bowl titles and two junior grand slam singles titles, the 2008 Australian Open and 2009 US Open.  Highlights of Tomic's career include winning the 2013 Apia International Sydney, 2014 Claro Open Colombia and the 2015 Claro Open Colombia.  Other highlights include a final appearance at the 2016 Acapulco Telcel and a quarterfinal appearance at the 2011 Wimbledon Championships as well as at the 2015 BNP Paribas Open and the 2015 Shanghai Masters. 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 professional Australian tennis player, Casey Dellacqua.  To date, Dellacqua has won eight career doubles titles: one grand slam mixed doubles title with Scott Lipsky at the 2011 French Open and seven WTA doubles titles including one Premier Mandatory doubles title with Yaroslava Shvedova at the 2015 Mutua Madrid Open.  Other highlights of Dellacqua's career include reaching the doubles finals of all four grand slams; a quarterfinal finish in singles at the 2014 BNP Paribas Open and fourth round appearances at the 2008 Australian Open and 2014 Australian Open and US Open respectively.  Dellacqua achieved a career high singles ranking of World No. 26 on September 29, 2014 and later achieved a career high doubles ranking of World No. 3 on February 1, 2016. Maria Yuryevna Kirilenko-Stepanova (Russian: Мари́я Ю́рьевна Кириле́нко ; ] ; born 25 January 1987) is a Russian tennis player.  Kirilenko won the 2002 U.S. Open Girls' Singles and won her first WTA Tour title in 2005, defeating Anna-Lena Grönefeld in the China Open.  She has reached three Grand Slam singles quarterfinals, at the 2010 Australian Open the 2012 Wimbledon Championships and the 2013 French Open.  In doubles, she has reached two Grand Slam doubles finals, at the 2011 Australian Open and the 2012 French Open, won the 2012 WTA Tour Championships and was a bronze medalist at the 2012 London Olympics.  In June 2013, Kirilenko reached her career high ranking of World No. 10. Stan Wawrinka was the defending champion, but he lost in the semifinals to Novak Djokovic.  Andy Murray and Novak Djokovic contested the final for the third time, having met for the title in 2011 and 2013 with Djokovic winning both times. 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. Jordan Thompson (born 20 April 1994) is an Australian professional tennis player, reaching a career high ranking of World No. 63 on 13 February 2017.  He made his grand slam debut at the 2014 Australian Open after winning the Australian Open wild card play off on 15 December 2013.  Thompson reached his first ATP quarterfinal at Brisbane in 2017, defeating David Ferrer en route. This is a list of the main career statistics of Japanese professional tennis player, Kei Nishikori.  To date, Nishikori has won 11 ATP singles titles including a record four consecutive titles at the Memphis Open.  Other highlights of Nishikori's career thus far include reaching the finals of the 2014 Mutua Madrid Open, 2016 Miami Open, 2016 Rogers Cup, and 2014 US Open, a semi-final appearance at the 2014 ATP World Tour Finals and 2016 US Open, quarterfinal finishes at the 2012 Australian Open, 2015 Australian Open, 2016 Australian Open and 2015 French Open.  Nishikori achieved a career high singles ranking of world No. 4 on March 2, 2015.
Answer: world No. 3