 Complete the following phrase:  In singles, Mahut reached a career-high ATP ranking of world No. 37 in May 2014, and has won four tour-level titles. All of these were on grass courts, where only Roger Federer 19, Andy Murray 8 and Novak Djokovic 5 have won more titles amongst active players. His best Grand Slam result in singles was at the 2016 Wimbledon Championships, where he reached the fourth round. At the 2010 Championships, Mahut was part of the 