Fish overcome his frustration at a close line call at the end of the first set Sunday to win his fourth career title. The fifth-seeded American entered the week ranked 79th.
"You've got to keep the goal in mind," he said of the point. "Not every call is going to be perfect. Everybody's trying to do their job. I felt like I was on the tough end (of that)."
On the final point of the first set, Rochus hit a return to the back corner. Fish appeared ready to play the ball and let it go. The chair umpire said Rochus won the game and set. Fish argued and waved his racket to the chair.
Fish took control in the best game of the match, breaking in the ninth of the third set to go up 5-4. He squandered three break points before closing it out with a forehand cross at the net.
"I wanted to play this match on my terms. I wanted to win it or lose it on my racket," he said of the key game. "I've certainly lost a lot of heartbreak finals. It certainly feels great to win one."
In the final game, Rochus failed on a pair of break point chances. On the final point, Rochus lunged on a wide serve, barely getting a backhand over the net before Fish put an easy forehand cross in to end it. He raised both arms in triumph, turned to the fans at all four sides of the court and gestured with a hug.
"You're bound to have a lot of nerves, I knew that," Fish said. "I've been in just about every situation, but it's been a long time."
His last title was in 2009 at Delray Beach, Calif.
The 29-year old Rochus entered the week ranked 65th. He hadn't lost a set this week until the finals.
"I can't say I did play a bad final, didn't go for it," Rochus said. "I went for it. The last two games were so close. Mardy was pushing hard at the end."
Fish had 24 aces in the match. Rochus had just two.
"That was the key of the match," Rochus said. "We know Mardy has a great serve."
Fish played in his second final in a month, improving his career mark to 4-11 with his first title on grass. He lost to Sam Querrey at Queen's Club in June.
Rochus fell to 2-6 in ATP finals. It was his first on grass.
Fish won $75,700 and Rochus earned $39,780.