Isner returned to Athens, Ga., where he starred for the University of Georgia, because it's the place where he's most comfortable in the world. He'd just been through some serious seismic activity, and he wanted a week to get back on solid ground, rest and relax and see a football game.
"It kind of sunk in then," Isner said of his breakout summer, in which he reached the final in Washington, D.C., against top American Andy Roddick and the third round of the Open against world No. 1 Federer within the space of a month. "I realized now that I'm playing so much better, I can compete with anyone in the world, and it's up to me to keep it up and see how far I can go."
The North Carolina native was talking during a quiet moment at the U.S. Davis Cup team's hotel in Gothenburg, Sweden, where he and Sam Querrey served as practice partners for the squad. The U.S. team defeated Sweden and earned a chance to play a home final for the first time in 15 years. Isner said he enjoyed the trip despite being ravaged early on by a stomach flu that carved 12 pounds off his 6-foot-9, 236-pound frame within a couple of days.
There's a chance his immune system is going to take a beating as he sets out on the nomadic ATP circuit -- Isner didn't play much junior tennis or travel outside the United States to compete. Instead, he stayed home and played tennis three or four times a week and led a normal teenaged existence. Neither that nor his ostensibly unconventional path through four years of college seems to be hurting him now.
"There's a lesson to be learned here for parents and coaches," said U.S. Davis Cup captain Patrick McEnroe, who was so impressed with Isner's performance in Washington that he invited him to Sweden on live television after the final.
"There are a lot of guys out there who probably should have gone to college, who are struggling," McEnroe said. "A big part of making it in professional tennis is how you deal with the emotional ups and downs, and there are a lot of downs, because you lose a lot."
The weekend Isner was back in Athens, his beloved Bulldogs fell to South Carolina. One of the charming -- and rather remarkable -- things about the towering 22-year-old is that the football team's loss bothered him far more than anything that has befallen him on the tennis court so far.
"I'm a huge sports fan, and when one of my teams loses, I'll go into my cave, my little shell, for a whole day," Isner said, stretching his long legs out in the players' dining area. "I've been known to break my phone a couple times. I get so nervous."
Yet in a match, what you see with Isner is what you get -- a seemingly unflappable competitor who is confident without being arrogant. He attributes his composure to playing four years at Georgia, where the pressure to perform in a team setting made playing solo a breeze by comparison.
"Now that I'm playing just for me, I didn't feel that much pressure at all," he said. "The only person I'm going to disappoint is myself. I'm not going to let anyone else down.
"I don't get flustered. I rarely get mad. This summer, every guy I played was ranked ahead of me and every match was a huge opportunity. I couldn't afford to get down on myself."
That was true even when Isner faced Federer, and won the first set in a tiebreak in a packed Arthur Ashe Stadium. Federer won the match in four sets, but Isner won morale points. "I went out there thinking I was going to win the match," he said. "He kind of figured me out and beat me down those last three sets, but there wasn't a single point of the match where I doubted myself."
Isner can't go anywhere without being picked out of a crowd. Tennis people know who he is, but most strangers assume, understandably, that he plays basketball, which he hasn't played since ninth grade.
Still, hoops has something to do with where Isner is now, according to Georgia coach Manny Diaz. Isner was nearly as tall as he is now when he played basketball, but 40 pounds lighter, and got knocked around a lot in the post.
"He was a kid who really wasn't intimidated by tough situations, very secure in who he was," Diaz said. "But the special thing about John is that he was never really one to put his self-worth on the line in a tennis match.
"A lot of kids get so tight in big matches, and see themselves relative to what they do on the court that day. John is one of the best competitors I've ever seen, in large part because he doesn't get caught up in 'What if I fail?' in big situations."
Isner knows that if he's successful on the ATP level, the dynamic will change and he'll be a marked man instead of the lovable underdog. He's currently ranked No. 144 and is playing in a Challenger event in Tulsa, Okla., this week. Isner plans to play other lower-level events in the U.S. this fall to try to boost his position enough to get into the Australian Open main draw.
Diaz predicted Isner's transition will be smooth. Isner rented an apartment in Tampa, Fla., the week after the NCAA championships and already has a circle of friends and mentors, thanks to his friendship with Bo Hodge, the ex-Georgia All-American who was one of Roddick's high school pals and now works with Mardy Fish.
James Blake also has taken Isner under his wing, although he wasn't crazy about the fact that Isner won a few hands of poker in Sweden.
"He fit right in with the guys, and there's this sense he feels like he belongs, in a good way," McEnroe said. "The stronger he gets, and put a little weight on him, I think he's going to be real dangerous."
Bonnie D. Ford is a frequent contributor to ESPN.com.