PHOENIX — Doug Davis made one early mistake before cruising to his fourth straight decision.

Davis allowed five hits over seven innings and Tony Clark homered and drove in two runs as the Arizona Diamondbacks beat the Pittsburgh Pirates 4-2 on Thursday night.

Davis gave up two hits in the first inning, including Jason Bay's homer that just cleared the fence in left field, but let only one batter reach second base over his final six innings.

"I've said it before and I'll say it again. I was one pitch away from greatness," said Davis, who struck out three and walked three. "It was a fastball middle-in instead of in and they took advantage of it."

Davis hasn't lost since giving up three runs in seven innings in a 3-2 loss to the St. Louis Cardinals on July 5.

Orlando Hudson drove in the go-ahead run in the seventh for the Diamondbacks, who won for the fifth time in six games and have won eight of nine series since the All-Star break.

Arizona is 15-3 since dropping consecutive games July 19-20 in Milwaukee and Chicago, and moved three games in front of San Diego in the NL West.

Brandon Lyon pitched the eighth and Jose Valverde came on in the ninth for his major league-leading 35th save in 40 chances.

Pinch-hitter Jeff Cirillo hit a double off reliever Shawn Chacon (4-3) in the seventh, his first hit for Arizona since he was claimed off waivers from Minnesota on Aug. 3. He went to third on a groundout by Chris Young, and Hudson followed with a hard bouncer through the drawn-in infield, scoring Cirillo and giving the Diamondbacks a 3-2 lead.

Pittsburgh took a 2-0 lead in the first. Freddy Sanchez doubled to left and Bay followed with his 18th homer.

"I think you're foolish if you think 2-0 is going to hold up in this league," Bay said. "Sometimes it is but it's not something you can rest on. We had a couple of chances to add on or even take the lead and we didn't do that."

The Diamondbacks tied it in the fourth against Ian Snell. Eric Byrnes, Chad Tracy and Clark hit consecutive one-out singles to pull Arizona within one, and Chris Snyder drove in Tracy on Arizona's fourth single of the inning to tie the game.

Snell allowed two runs and six hits in six innings, with three walks and seven strikeouts.