Alone atop the National League West standings for the first game series tonight versus the Houston Astros at Chase Field.

The Diamondbacks leaped over the San Francisco Giants to take a half-game lead in the division with Wednesday's 6-3 victory. The Giants were beaten by Pittsburgh earlier in the day to lose their grip on NL West bragging rights.

Rookie pitcher Josh Collmenter turned in a solid performance for Arizona with seven innings of two-run ball and five strikeouts, evening his record at 7-7. He scattered four hits and walked only one batter before Bryan Shaw allowed a run in the eighth and David Hernandez closed the door in the ninth inning for his 10th save of the season.

Paul Goldschmidt singled in two runs, Willie Bloomquist homered and both Chris Young and Gerardo Parra each knocked in a run for Arizona, which is alone atop the NL West for the first time since June 24.

It is also the latest the D'Backs have been in first place since Sept. 5, 2008.

"We still got a long season in front of us," said Arizona outfielder Justin Upton, who finished with three hits and a run scored. "I just hope we can stay there for a little bit longer than a couple days this time."

Upton is a big reason why his club is back in first place and has hit safely in 18 of his last 21 games. He is batting .373 during the run with 10 doubles, two triples, eight homers and 26 runs batted in. Arizona has won two in a row, three of four and 11 of the past 17 games, and is 303 so far on a 10-game homestand with the New York Mets slated to visit the desert this weekend.

Joe Saunders will take the mound for the Diamondbacks tonight and looks to get back into the win column after he lost to Los Angeles on Saturday. He allowed four runs -- three earned -- and eight hits in 5 1/3 innings of that 5-3 loss to fall to 8-9 in 23 starts with a 3.61 earned run average. He had won two straight starts and five of six decisions before losing to the Dodgers.

Saunders, a left-hander, is only 2-5 in 11 starts at home this season and faced Houston for the first time in a 6-5 loss last Sept. 4. He did not record a decision in that one and limited the Astros to a pair of runs and three hits in seven innings of work.

Houston is aiming for a series split with Arizona and has dropped five of six and 14 of its last 19 games. In last night's three-run defeat, starter Henry Sosa made his major league debut and was roughed up for four runs -- three in the first inning -- and six hits in six innings with four K's and three walks.

"The first inning I overthrew the ball a little bit," Sosa said.

Carlos Lee, Humberto Quintero and Clint Barmes each had an RBI for the Astros, who had scored nine runs in each of the previous two matchups with Arizona and blew a 7-1 advantage on Tuesday. Quintero is riding a career-high 10-game hitting streak. Houston will visit Dodgers Stadium over the weekend.

The Astros will send Brett Myers to the mound tonight and he's 0-6 with a 4.79 earned run average in his last nine starts, with his club going 2-7 in that stretch. Myers, who hasn't won since June 17 at the Dodgers, lost to Milwaukee in a 7-5 setback on Saturday and allowed six runs -- five earned -- and 11 hits over six innings to fall to 3-12 with a 4.76 ERA in 24 starts.

Myers has recorded a 2-5 mark in 13 road starts this season and will face Arizona for the 10th time in his career. Over the first nine appearances, eight of which have been starts, the righty is 2-2 with a 4.26 ERA. He did not record a decision in a 7-6 home loss to the D'Backs back on May 27, when he was reached for four runs and five hits in 5 2/3 frames.

Arizona swept a three-game series with Houston from May 27-29 at Minute Maid Park and has won 13 of the past 17 matchups in this series.