CINCINNATI (AP) - For six innings, Edgar Gonzalez dominated the Cincinnati Reds. With one swing, Adam Dunn changed everything.

Gonzalez held Cincinnati hitless into the seventh, but Dunn's 39th homer on a 3-1 changeup helped the Reds rally for a 6-2 victory over the Arizona Diamondbacks on Sunday.

''That was the only pitch he gave me that I could really hit,'' Dunn said.

Ryan Freel drove in the go-ahead run with an eighth-inning single and the Reds avoided a three-game sweep.

Gonzalez faced the minimum 18 batters through six innings before Freel led off the seventh with a walk. Felipe Lopez followed with a chopper to first baseman Shea Hillenbrand while Freel was breaking for second and was credited with an infield single when Gonzalez failed to cover the bag.

''I didn't see the runner going,'' Gonzalez said. ''I thought (Hillenbrand) was going to go to second base. Then I saw him look toward first, and I started too late.''

That miscue cost Gonzalez and the Diamondbacks.

''It leaves a little bit of a bad taste, but it will happen,'' Arizona manager Al Pedrique said. ''Late in the game, we didn't execute defensively. You're not going to play perfectly every day.''

Sean Casey then hit into a double play, but Dunn's two-run homer gave the Reds a 2-1 lead.

''I wanted that pitch down in the zone, but it was right down the middle,'' Gonzalez said. ''I tried to get him to roll over on a changeup and get a groundball.''

Dunn stayed confident even as the Reds struggled at the plate against Gonzalez.

''I knew we'd get to him, eventually,'' Dunn said. ''He made great pitches all day, but you knew he'd make a mistake.''

Scott Hairston tied the game with his 12th homer in the eighth off Todd Van Poppel (4-5), who ended up with the win.

Juan Castro started the eighth-inning rally against reliever Mike Fetters (0-1) with a one-out single. Pinch-hitter Jacob Cruz followed with a walk and Freel grounded a single through the hole into left field for a 3-2 lead.

The Reds added insurance runs when pinch-runner Wily Mo Pena scored on Hillenbrand's throwing error and on bases-loaded walks by Shane Nance to D'Angelo Jimenez and Lance Cormier to Austin Kearns.

The game was scoreless until the sixth, when Luis Terrero hit a double to left-center and scored on Jerry Gil's bloop single for Arizona.

Gonzalez was demoted to the bullpen after his 3-1 loss at Pittsburgh last Tuesday left him 0-7 in seven major league starts this season. He got another chance when Stephen Randolph was scratched from Sunday's start with stiffness in his right shoulder.

''(Gonzalez) had really good stuff, but nothing you would think would no-hit us for six innings. We should've gotten to him a lot earlier. We didn't square him all day until Dunn's two-run (shot),'' Casey said.

Gonzalez allowed a career-low three hits and two walks with three strikeouts in seven innings.

''He was working faster,'' Pedrique said. ''He improved a lot in that area. He did a great job, and he deserves another start. The way he pitched today, I thought he should've won.''

Cincinnati starter Josh Hancock matched his career high of six strikeouts by the fifth inning. He allowed one run on seven hits and two walks in six innings.

Notes: Ken Griffey Sr., the right fielder on the Reds' 1975-76 World Series championship teams, Bob Howsam, Cincinnati's general manager in that era, and 1800s pitcher Will White were inducted into the team's Hall of Fame in pregame ceremonies. … Reds RHP John Riedling celebrated his 29th birthday. … Arizona catcher Chris Snyder was hitless in his last 10 at-bats before his second-inning single. … Hillenbrand's error was Arizona's 107th of the season, tying a club record set twice previously.