Considered one of the best servers ever to play on the ATP Tour, Isner achieved his career-high singles ranking in July 2018 by virtue of his maiden Masters 1000 crown at the 2018 Miami Open and a semifinals appearance at the 2018 Wimbledon Championships. He has also twice reached the quarterfinals at the US Open in 2011 and 2018, the latter of which helped qualify him for his first ATP Finals appearance later that year. He currently has the second-most aces in the history of the ATP Tour, having served over 13,000 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, played over the course of three days. Isner currently holds the record for hitting the ATP's fastest "official" serve ever and third-fastest on record in tennis at during his first-round 2016 Davis Cup match. On 17 August 2021 at the 2021 Western &amp; Southern Open, he became only the second player in the world to reach 13,000 aces on the most aces in career list (not including Davis Cup), joining Ivo Karlovic.