He reached the semifinal of the 2008 Tour Finals. Simon reached the 4th round of the French Open in 2011, 2013, and 2015 as well as the 4th round of the US Open in 2011 and 2014. He reached the 3rd round of the Olympic Games in 2008 and 2012. Simon won the Davis Cup in 2017. His wins include the Romanian Open, the Indianapolis Tennis Championships, the Thailand Open, the Sydney Invitational, and more.