SAN FRANCISCO -- Matt Moore isn't scheduled to pitch for the San Francisco Giants in their big four-game series against the Chicago Cubs that starts Thursday.

So he made sure Wednesday not to set his club back even before it stepped into Wrigley Field.

Moore recorded his first home victory since being traded last month, and batterymate Buster Posey drove in two runs with a double and a sacrifice fly, leading the Giants to a 4-2 victory over the Arizona Diamondbacks and a split of their two-game series.

Joe Panik had three singles in a nine-hit attack as the Giants spoiled the major-league return of Diamondbacks right-hander Shelby Miller.

"It does feel like we're playing for something," Moore said after the Giants recorded their 72nd win, fourth-most in the National League. "I want to contribute."

Posey and Hunter Pence drove in first-inning runs against Miller, who was returning from an eight-week stint at Triple-A, to give the Giants a lead they never relinquished en route to their third win in five games on their just completed homestand.

The two runs were all Miller (2-10) allowed in six innings. He gave up six hits, walked one and struck out three.

"I was kind of a little jittery there in the first inning, just getting back in that atmosphere which is always so much fun," admitted Miller, whose ERA dipped from 7.14 to 6.81. "That first inning was good to get under my belt, and then I did a good job settling in."

Posey's sacrifice fly came in a two-run seventh inning that turned a 2-1 margin into a three-run advantage. Pinch-hitter Conor Gillaspie had a triple and Angel Pagan a double in the inning.

Moore (9-10) held the Diamondbacks to one run on five hits in 5 1/3 innings. He walked one and struck out seven.

The left-hander had suffered 8-5 and 9-5 losses in his first two home starts for the Giants, yet still was given generous ovations both before and after his first San Francisco success.

He was coming off 8 2/3 innings of no-hit ball last Thursday on the road against the NL West-leading Los Angeles Dodgers.

"It feels great to be accepted," Moore insisted. "It's great to have that kind of support behind you."

A.J. Pollock singled, stole a base and scored on an infield out in the sixth inning for Arizona's only run against Moore.

The Diamondbacks threatened against the San Francisco bullpen in the eighth inning, loading the bases on a Jean Segura double and two walks against Sergio Romo.

But Giants closer Santiago Casilla was summoned with two outs and the bases loaded, and he struck out Yasmany Tomas to strand the potential game-tying runs on the bases.

"They had a hot hitter up there. He's hit a lot of home runs," Bochy said of Tomas. "Casilla saved us there. That's huge."

Casilla gave up a two-out solo home run to pinch-hitter Jake Lamb in the ninth and a hit to Segura, his third, before locking down his 29th save.

The homer was Lamb's 26th of the season.

"The biggest thing for us is to capitalize on these last games and try to play great baseball," Miller said of the split. "It's good to be back helping."

Brandon Crawford and Gorkys Hernandez also doubled for the Giants, who recorded five extra-base hits among their nine total.

Hernandez, subbing for Denard Span in center field, also made the defensive play of the game, snatching a Paul Goldschmidt drive inches before it hit the fence in the sixth inning. Pollock was on first base with no outs in a 2-1 game at the time.

"He's a gifted outfielder. That's why he played today," said Bochy, whose club played its 15th consecutive error-free game. "I wanted our best outfield out there. He saved us, too."

Despite the win, the Giants finished August with just an 11-16 record, their worst month of the season.

Brandon Drury had two hits for the Diamondbacks, who won the series opener 4-3 on Tuesday night.

"It's a step in the right direction," Diamondbacks manager Chip Hale said of Miller's effort. "It's good to see him pitch against these (contending) teams."

Arizona stole three bases in the game and finished the month with a club-record 42.

NOTES: The Diamondbacks' sixth-inning run snapped LHP Matt Moore's scoreless streak at 16 2/3 innings. ... The pinch-hit home run by Diamondbacks 3B Jake Lamb was the second of his career. He also connected May 27 against San Diego. ... Diamondbacks RHP Randall Delgado was charged with both Giants runs in the seventh inning. He hadn't allowed a run in his previous 14 games. ... In order to create a spot for RHP Shelby Miller on the active roster, the Diamondbacks demoted RHP Vicente Campos to Triple-A Reno. ... Giants manager Bruce Bochy admitted after the game he is still not sure who his club will start Friday in Chicago. RHP Albert Suarez is the manager's first choice, if he is not needed in relief Thursday. ... Giants CF Denard Span (stiff neck) was given the day off.