Isner reached the fourth round of the French Open. At Wimbledon, he advanced to his first quarterfinal at a Slam in seven years since 2011 US Open. In the quarterfinal, Isner defeated Milos Raonic in four sets to advance to the first Grand Slam semifinal of his career, in which he lost to South African Kevin Anderson in a long five-set match. This match lasted 6 hours and 36 minutes with a final score of 7–6, 6–7, 6–7, 6–4, 26–24, which was the fourth-longest match in history and the second-longest at a Grand Slam tournament behind Isner's first round defeat of Nicolas Mahut in 2010, also at Wimbledon. Isner adopting and working on an aggressive return style and a strong serve-and-volley game have been cited as reasons for his success in 2018 at Wimbledon.