PARIS - This, then, is who John Isner is for now: The Marathon Man of Tennis, the guy who plays and plays and plays, for hours on end, until the last set seems interminable.At Wimbledon two years ago, he won 70-68 in the fifth, the longest set and match in tennis history. At Roland Garros on Thursday, as afternoon gave way to evening, the 10th-seeded American lost 7-6 (2), 4-6, 4-6, 6-3, 18-16 to Paul-Henri Mathieu of France in the second round, a 5-hour, 41-minute test of stamina and attention span.This one goes in the books as the second-longest match, by time, in French Open history.‘’I just didn’t get it done. I felt like I got caught in patterns that weren’t ideal for me,’’ said a somber Isner, whose exit means there are no U.S. men in the third round for the first time since 2007. If the 6-foot-9 Isner, is going to become more than a novelty act, he needs to win encounters like Thursday’s, and not because of the duration but because it was a first-week Grand Slam match against a player ranked 261st who got into the field thanks to a wild-card invitation from the tournament.After finally converting his seventh match point - Isner never had one - an emotional Mathieu thanked the partisan crowd in the main stadium for willing him to victory. ‘’I dug deep,’’ said the 30-year-old Mathieu, who hadn’t played in a major tournament since the 2010 U.S. Open because of a left knee injury that forced him off tour all of last year. ‘’I was away from the courts for quite a while, and I came back to live moments like this.’’