HOUSTON -- Ryan Hanigan wanted to make sure baseball's instant replay system wouldn't start for a few more days.
Hanigan broke the tie in the eighth with a one-out homer off Geoff Geary that bounced off the facade in left center, just above the yellow line. Second-base umpire Ted Barrett made the home run signal and Houston manager Cecil Cooper came out to talk to him.
Baseball announced Tuesday it will start using video to clarify "boundary calls," including whether fly balls went over the fence, but the system won't start until Thursday.
"It's not in place tonight, right?" Hanigan asked. "They called it a home run at first, so I didn't think they were going to change it. But, hey, if those are the rules, those are the rules you play by."
All Cooper could do was protest to no avail. He is a proponent of the new system.
"It was a home run," Cooper said. "From my seat, I thought it wasn't at first. But after I went out and argued with him and talked with him a little while, he said he definitely saw it. But I definitely think we still need replay."
Arroyo (12-10) allowed five hits and struck out three for his first complete game since May 16, 2007. Arroyo snapped a four-game losing streak to Houston when Lance Berkman flied out to center for the last out.
Berkman came into the game with a .324 average against Arroyo, but went 1-for-4 with a single and a strikeout.
"It was actually nice to have him out there," said Arroyo, who threw 109 pitches. "He's beaten me so many times. I felt good against him all night."
The Reds were the last team without a complete game this season, a distinction that had started to nag Arroyo and the other starters.
"We were aware of that," Arroyo said. "Even if you're having an off year, you're going to sprinkle a few in here and there. We got one, so at least we get off the schneid for a season."
Geary (2-3) relieved Houston starter Wandy Rodriguez, who had a career-high 10 strikeouts and allowed three hits over seven innings.
Both starters breezed through the first three innings without allowing a hit. Rodriguez struck out four and Arroyo two.
Chris Dickerson got the game's first hit when he led off the fourth with a single up the middle. Jeff Keppinger lined Rodriguez's next pitch into the left-field corner for a double.
With Houston's infield in, Brandon Phillips hit a hard grounder to first that Berkman dived to stop. Berkman beat Phillips to the base, but Dickerson scored to put the Reds up 1-0.
Miguel Tejada singled with one out in the Houston fourth. Berkman struck out on a 3-2 pitch and Hanigan threw out Tejada trying to steal second for a double play.
Mark Loretta led off the Houston fifth with a single to left and Hunter Pence walked. Both advanced on David Newhan's groundout and Loretta scored on Brad Ausmus' groundout to tie the game 1-1.
Rodriguez struck out Phillips looking leading off the seventh. Joey Votto singled to right, but Rodriguez fanned Edwin Encarnacion for his ninth strikeout, tying his career high. Jay Bruce then swung and missed at a curveball, striking out for the third time.
"Wandy was fantastic," Cooper said. "His command was good, his breaking ball was good. He was attacking the bottom of the strike zone."
Berkman blooped a single to left leading off the seventh. Phillips then made a diving stop on Loretta's grounder and flipped to Keppinger, the shortstop, for the force at second. Pence then grounded into a double play, the Reds' third of the game.
"That was real big," Arroyo said of the double plays. "These guys played a really good defensive game."
Hanigan's second homer of the season was only the third allowed by Geary in 58 innings this season.
"I threw a bad pitch," Geary said. "It was bad location and he hit it well."
The Reds beat the Astros for just the second time in 10 meetings this season.
Arroyo has six complete games in his career. ... Geary allowed a run for just the ninth time in 48 appearances this season. ... RHP Francisco Cordero missed Tuesday's game to be with his new son, Michael Javier, who was born on Sunday. Cincinnati manager Dusty Baker expected Cordero to rejoin the team Wednesday.