The closer issued an intentional walk with two outs in the ninth inning to load the bases, then retired Dunn on a grounder that preserved the Rockies' 6-5 win over the Arizona Diamondbacks on Wednesday.
"I'm going to pitch to my strengths 99 percent of the time, and especially in that situation," Fuentes said. "I'm not going to get beat with my third-best pitch."
The Diamondbacks rallied within a run in the ninth on Stephen Drew's RBI single. With runners on second and third, Fuentes walked Conor Jackson to bring up Dunn.
"You never get many better finishes than that," Rockies manager Clint Hurdle said. "Putting a guy on base to face a guy tied for the lead in home runs. That's a classic confrontation there."
Dunn, acquired from Cincinnati on Monday and tied for the major league lead with 32 home runs, grounded out to shortstop Troy Tulowitzki on a 3-2 fastball.
"I hit the 3-2 pitch good, but I beat it in the dirt," Dunn said. "I don't get many hits when I hit it on the ground."
Dunn was 1-for-5 in his second game with the Diamondbacks.
"Adam hit the ball right on the screws, but they were playing him up the middle," Arizona manager Bob Melvin said. "We had our opportunity. The big out was the strikeout of Chris Young."
It was just the Rockies' second win over the Diamondbacks in 11 games this season.
"We'd only beaten them one time before tonight," Hurdle said. "We needed to win a ballgame."
Chad Tracy homered for Arizona, which started the day in first place in the NL West.
It was 4-all when Chris Iannetta led off the Colorado eighth with a double. After pinch-runner Cory Sullivan moved to third on a sacrifice, Hawpe connected against Jon Rauch (4-3) for his 19th home run.
"I was looking for a fastball up," Hawpe said. "I know in the past they've tried to beat me with fastballs up and in."
Taylor Buchholz (5-3) pitched the eighth inning and Fuentes held on for his 22nd save in 26 chances.
Colorado starter Jeff Francis gave up three runs and six hits and remained winless since June 18. After posting 17 victories last season for the NL champions, he has only three wins this year.
"I started off really good again, but the things I've been working on mechanically I got away from in the fifth, sixth inning," Francis said.
Arizona scored twice in the seventh to tie it at 4. Chris Snyder led off with a double, and Manny Corpas relieved Francis. Tony Clark had an RBI grounder, and a double by Drew and a single by Young produced another run.
Stewart led off the second with his seventh home run to make it 3-0.
Tracy made it 3-1 when he led off the fifth with his eighth home run of the year. Barmes hit his sixth homer leading off the bottom half.
- Rockies LHP Glendon Rusch will pitch Thursday in place of Aaron Cook, who will miss the start with lower back stiffness.
- Rockies INF Garrett Atkins missed his second straight game with strep throat.
- Taveras stole his 52nd base of the season, one short of Eric Young's franchise record set in 1996.
- Drew extended his hitting streak to 15 games.