Fish has lost 30 pounds since having knee surgery last year, and he credits his newly gained fitness for his winning streak which continued Sunday when he beat John Isner 4-6, 6-4, 7-6 (7-4) in the finals of the Atlanta Tennis Championships.
Fish set personal bests by winning his second straight tournament and 10th straight match.
Fish overcame temperatures in the mid-90s as the match lasted 2 hours, 45 minutes. The on-court temperature hovered near 150 degrees.
Suffering from dehydration, Fish needed an IV after the match and had a long visit to the trainer's room. He said he "sort of went into a lower body cramp with both legs."
A year ago, he said he'd would have had no chance.
"It's night and day," Fish said. "A year ago I would have fallen over in the second set probably, or probably played a match to where I knew physically I couldn't last so I needed to change my tactics. I just simply don't have to do that anymore."
Isner, a former college star at the nearby University of Georgia, had no home-state advantage when dealing with the heat.
"The first hour it was the hottest," Isner said. "It took a lot out of both of us. I don't think I've ever played in conditions this hot and humid and rough like this."
Fish, who won in Newport earlier this month, took the first four points of the tiebreaker.
"I knew the way we were both feeling a good start in the tiebreaker was going to be huge," Fish said.
Isner rallied to win the next three points but couldn't pull even.
Isner gained fame by winning the longest match in history, a three-day, 183-game match at Wimbledon last month. That match led to appearances on TV talk shows, and he says he spent too much time away from the court.
"You want to win this tournament but it was really pivotal I was able to get four matches under my belt," Isner said. "I had other things I was doing because of that stupid Wimbledon match I played."
Isner is 1-3 in finals this season.
"It's disappointing," he said. "I've made four finals this year and I've lost my last three, all in three sets. That's tough to swallow but it hasn't stopped me from progressing."
Isner had the backing of many Bulldogs fans who wore Georgia caps and shirts and barked in support of the local favorite.
Fish didn't drop a set in winning his first four matches in Atlanta, including his upset win over top seed Andy Roddick in the semifinals. For a change, Fish fell behind when the 6-foot-9 Isner won the opening set.
Fish, the No. 6 seed who is ranked 49th in the world, fought back against Isner, the No. 2 seed. He broke Isner's serve for the first time to win the second set and then broke again for a 3-1 lead in the third set. Isner answered by breaking Fish and then held serve to pull even.
Isner played in the heat of the day throughout the tournament while Fish drew evening matches.
Isner wouldn't say the schedule favored Fish.
"It's hard to say," Isner said. "You could make a case that it took a toll on me. You could make a case that it was a disadvantage to him because he wasn't used to it."
The Atlanta tournament was accompanied by the first of 10 summer events in the U.S. Open Series. Sixteen players are competing for a wild-card spot in the U.S. Open qualifying tournament.