John Robert Isner is an American professional tennis player who has been ranked as high as No. 8 in men's singles by the Association of Tennis Professionals (ATP). 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 12,000 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 157.2 mph or 253 km/h during his first-round 2016 Davis Cup match.