It stretched over three days before Isner won 70-68 in the fifth set.
The rematch is Tuesday at the All England Club. Fittingly, perhaps, Isner-Mahut II might not finish today. That's because it's the fourth match on tap for Court 3 -- and the forecast calls for rain.
Court 3 holds 1,980 spectators, about 1,200 more than tiny Court 18, which now bears a plaque noting it was the site of the 2010 match.
The rematch has been the talk of the tennis world ever since they were randomly selected to face each other again in the first round in Friday's draw.
Rafael Nadal said that when he heard the news, he felt "sorry for them."
Andy Murray suggested in a tweet that this year's match between the American Isner and France's Mahut should be on Centre Court.
"Their match last year was incredible. It's not going to happen again. It will never happen again," Murray said. "I feel for them a little bit that people might be hyping the match up a lot, and it's not going to be the same scoreline."
BRITAIN'S HOPE: One message read: "Believe in yourself and never give up." Another simply said: "Make history."
The words of support from Facebook fans printed on Andy Murray 's racket bag looked as if they might be having the opposite effect Monday when he dropped his first set at Wimbledon.
Then Murray reeled off 15 consecutive games for a 4-6, 6-3, 6-0, 6-0 win over Daniel Gimeno-Traver to reach the second round.
Murray is once again carrying the hopes of the home nation, desperate for the first British male champion at Wimbledon since 1936. The 24-year-old from Scotland has reached the semifinals the past two years, and he has raised hopes again by making the French Open semifinals and winning the grass-court title at Queen's Club last week.
TURNAROUND: After blowing a big lead and losing at the French Open, 19-year-old Christina McHale made sure she didn't make the same mistake at Wimbledon.
The resident of Englewood Cliffs, N.J., reached the second round at the All England Club for the first time -- and at any Grand Slam tournament for only the second time -- by eliminating 28th-seeded Ekaterina Makarova of Russia 2-6, 6-1, 8-6 Monday.
Last month in Paris, McHale led Sara Errani of Italy 5-0 in the third set before losing 6-7 (4), 6-2, 9-7.