PHOENIX -- The first time San Francisco visited Arizona this season, the National League West was up for grabs.

It is much closer to grabbed now.

One game separated the top four teams in the division when San Francisco touched down at Sky Harbor Airport to begin a four-game series in Arizona on May 12. None was off to a fast start. The Giants and Dodgers were .500 and tied for the lead, and the Diamondbacks and Rockies were two games below .500 and one game back. San Diego was within 2 1/2.

The Giants swept that four-game series and used it as a springboard to a 31-10 run that has given them the second-best record in the NL and a recent eight-game division lead that dropped to six over Los Angeles when Oakland took three of four in the Bay Area series that ended Thursday. Colorado sits 11 1/2 games out while Arizona is 14 and San Diego 16.

Neither the Giants (50-31) nor the Diamondbacks (36-45) have much momentum entering this three-game series that begins Friday in Chase Field, when winter targets Johnny Cueto (11-1) and Shelby Miller (2-7) meet.

While the Giants salvaged the final contest of the four-game home-and-home set against the A's, Arizona lost three straight at home to Philadelphia, taking some of the luster off a franchise record-tying 7-3 road trip leading into the Phillies series.

The Diamondbacks also might have lost-righter Zack Greinke in the process. Greinke left Tuesday's start against Philadlephia with soreness in his left oblique muscle. The D-backs believe they removed Greinke before the injury worsened, but they do not know if he can make his next start Monday. They are expected to make a decision Friday.

The Giants swept the May 12-15 series without using Madison Bumgarner, and the D-backs will miss Bumgarner again this time around. Bumgarner beat the A's 12-6 on Thursday and he was 1-for-4 with a double that ignited a six-run third inning. Bumgarner hit for himself in the game played in Oakland, the first time a pitcher intentionally was used instead of a DH since left-hander Ken Brett batted for the White Sox in 1976.

The Diamondbacks have underachieved at the halfway point, and a lot of it can be traced to their play at home, where they are 13-28. Only Atlanta (12-32) has a worse record.

"Obviously I think if you asked everybody that question, we're pretty disappointed on how the first 81 games have gone," Arizona setup man Daniel Hudson said. "There's a lot of baseball left to be played. Hopefully we can get it turned around quick and put some pressure on some other teams."

The Giants are 26-15 on the road, the best record in the league, but will be without three regulars this weekend. Hunter Pence (hamstring) has been on the disabled list since June 2 is not expected back until late in the season. Matt Duffy (Achilles) and Joe Panik (concussion) recently went on the DL.

While the NL is rich in third basemen, Arizona's Jake Lamb is making a push for All-Star consideration. Lamb has 17 homers and 55 RBIs and is leading the team in both categories. He had nine homers in June, second-most in franchise history behind Luis Gonzalez (12 in 2001).

Giants shortstop Brandon Crawford is 21-for-64 with 20 RBIs in his last 18 games.