Question: Does Nicolas Mahut or Elena Bovina have the highest career singles world ranking?
Context: Sonchat Ratiwatana (Last name pronounce : Ra-Ti-Wat) (Thai: สนฉัตร รติวัฒน์ 'ต้น') (born January 23, 1982 in Bangkok) is a professional tennis player from Thailand.  In 2007, Sonchat and his twin brother Sanchai Ratiwatana won their first ATP doubles title in Bangkok in their home country.  In the final, the team beat 2007 Wimbledon men's doubles winner Michaël Llodra and 2007 U.S. Open men's doubles semifinalist Nicolas Mahut.  He reached his highest doubles ranking at world number 39 as of 28 April 2008.  He plays right-handed and turned professional in 2004.  He and his twin brother played in their first grand slam tournament during the Australian Open in 2008, where they lost to the eventual finalist pairing of Arnaud Clément & Michaël Llodra of France in the first round. Nicolas Mahut and Édouard Roger-Vasselin were the defending champions, but Roger-Vasselin chose not to participate.  Mahut played alongside Sergiy Stakhovsky, but lost in the semifinals to Jonathan Erlich and Rajeev Ram. <br> Elena Olegovna Bovina (Елена Олеговна Бовина ) (born 10 March 1983) is a professional tennis player from Russia.  She reached her career-high singles ranking of World No. 14 in April 2005.  Her best performance at a Grand Slam came when she got to the quarter finals of the 2002 US Open, defeating Clarisa Fernández, Jelena Dokic, Stéphanie Foretz and Francesca Schiavone before losing to Lindsay Davenport. Elena Bovina and Rennae Stubbs were the defending champions, but had different outcomes.  While Bovina did not compete this year, Stubbs pertnered with Cara Black and successfully defended her title, defeating Elena Likhovtseva and Magdalena Maleeva 6–0, 6–1 in the final.  It was the 2nd title in the year for the pair, and the 14th title for Black and 44th title for Stubbs, in their respective careers. Nicolas Mahut and Édouard Roger-Vasselin were the defending champions, but only Mahut chose to compete in the doubles' rivalisation. Nicolas Mahut and Vasek Pospisil were the defending champions, but Pospisil chose not to participate this year.  Mahut played alongside Pierre-Hugues Herbert, but lost in the semifinals to Ivan Dodig and Marcel Granollers. The 2002 Challenge Bell was a tennis tournament played on indoor carpet courts at the Club Avantage Multi-Sports in Quebec City in Canada that was part of Tier III of the 2002 WTA Tour.  It was the 10th edition of the Challenge Bell, and was held from September 16 through September 22, 2002.  Elena Bovina won the singles title. Nicolas Pierre Armand Mahut (] ; born 21 January 1982) is a French professional tennis player.  In singles, he reached a career-high Association of Tennis Professionals (ATP) ranking of world No. 37 on 5 May 2014.  In doubles, he reached a career-high ATP ranking of world No. 1 on 6 June 2016.  Mahut is well known for being skilled on grass, on which he has won the third-most number of titles amongst active players in singles behind Roger Federer (15) and Andy Murray (8) and tying with Rafael Nadal (4); he also has the most singles titles on grass won over the age of 30 amongst active players, tying with Federer (4).  He is a distinguished doubles player, having been ranked world No. 1, and has reached all four Grand Slam finals in men's doubles, including winning the 2015 US Open and 2016 Wimbledon men's doubles titles. John Robert Isner (born April 26, 1985) is an American professional tennis player who is currently ranked world No. 17 in men's singles by the Association of Tennis Professionals (ATP).  Considered one of the best servers of the ATP World Tour, Isner achieved his career-high singles ranking of world No. 9 in April 2012.  In 2013, he became the 18th player to serve more than 5,000 aces on the ATP World Tour.  He currently has 4th-most aces in the history of ATP, having served more than 8,800 aces.  At the 2010 Wimbledon Championships, he played the longest professional tennis match in history, defeating Nicolas Mahut in a total of 11 hours and 5 minutes of play over the course of three days.  He also played the then 10th-longest singles match, a 5-hour 41-minute encounter in the second round of the 2012 French Open. Pierre-Hugues Herbert (] ; born 18 March 1991) is a French professional tennis player.  In doubles, he won the title at the 2015 US Open and 2016 Wimbledon as well as several Masters 1000 tournaments along with Nicolas Mahut.  In singles he has reached one ATP career final (at the 2015 Winston-Salem Open), and achieved his career high singles ranking of World No. 64 on 14 August 2017.
Answer: Elena Olegovna Bovina