Associated Press

Helmets fly as Arizona Diamondbacks' John Hester, left, collides with Houston Astros catcher Jason Castro on a play at the plate to end the fifth inning Sunday in Phoenix. The Astros defeated the Diamondbacks 3-2. Ralph Freso/AP Photo.

PHOENIX — Get rid of the first eight games of the season and the Houston Astros would be a .500 team.

Unfortunately the first week of the season does count in the standings and the Astros are eight-games under after Hunter Pence’s three-run home run in the first inning helped them beat the Arizona Diamondbacks 3-2 on Sunday.

“They don’t let us go back and do that over again,” manager Brad Mills said. “We’ve got to play with what we’ve got and go from there.”

Pence drove a pitch from Rodrigo Lopez over the right-field fence for his team-high 22nd homer of the season. Michael Bourn walked to lead off the game and Jeff Keppinger followed with a single before Pence’s homer.

“Bad location,” Lopez said of the pitch. “If I could have gotten it down I might have gotten a ground ball, but who knows?”

The hit was all the Astros (64-72) needed from their offense on the day. Starter J.A. Happ (6-2) held the Diamondbacks to two runs on six hits over seven innings to get the win, his third straight as an Astro after coming over in a trade with Philadelphia for pitcher Roy Oswalt. Happ struck out seven and worked out of a jam in the seventh, striking out John Hester and pinch-hitter Ryan Roberts with runners on first and second and one out.

“Fastball command is big. I’m starting to get dialed in more and more as each outing goes with the command,” Happ said. “The fastball and the changeup were good for me (Sunday).”

Hester, Arizona’s backup catcher, hit his second home run of the season, a solo shot in the third. Kelly Johnson added his 20th home run in the fourth.

The Diamondbacks trailed by one and had runners on first and second with two out in the fifth when Stephen Drew singled deep in the hole at second base. The runner at second, Hester, attempted to score but was easily thrown out at home.

“I saw (third base coach Joel) Youngblood waving me home so I kept going,” Hester said. “If I am safe, it ties the game, but I was out by a long way. Maybe I should have stayed at third.”

Lopez (5-13) settled down and worked six innings, not allowing a run after the first, but still hasn’t won a game since July 8. Lopez leads the majors with 33 home runs allowed and 99 earned runs allowed.

Matt Lindstrom worked a scoreless eight and Brandon Lyon converted his 13th save in 14 opportunities for the Astros, winners of 11 of their past 14 games. Arizona had a runner in scoring position with less than two outs in each of the last three innings but failed to push a tying run across.

“How good was Happ?” Mills said. “He threw the ball extremely well and kept his pitch count down...It was nice to see him get the outs with runners in scoring position as well.”

Notes: Diamondbacks third baseman Mark Reynolds aggravated a bone bruise in his right hand that affected his grip on the ball and took himself out of the game before the ninth inning, replaced by Augie Ojeda. ... Outfielder Justin Upton remains day-to-day after not being in the lineup Sunday because of left shoulder irritation. Upton has missed the past four games. Gerardo Parra has played right field in Upton’s absence Astros RHP Felipe Paulino threw a two-inning, 43-pitch simulated game Saturday at Chase Field with no setback. He’s on the 60-day disabled list with a right rotator cuff injury.