PHOENIX -- Geraldo Perdomo went 3 for 3 with a double, a triple and two RBIs, Zac Gallen pitched six smooth innings and the surging Arizona Diamondbacks beat the San Francisco Giants 8-1 on Monday night.

Arizona, which has won three straight and 12 of 18, moved a half-game ahead of San Francisco for third place in the NL West, just 1 1/2 games behind the idle New York Mets for the last National League wild card.

Gallen (12-14) allowed one run and two hits with six strikeouts.

Ildemaro Vargas' two-run single gave the Diamondbacks a 3-1 lead in a six-run sixth. Jordan Lawlar doubled in a run, James McCann hit a two-run homer and Perdomo added an RBI triple to make it 7-1.

Perdomo also walked twice on a perfect night at the plate in the leadoff spot.

The Giants mustered only two hits, matching their season low in a July 29 loss to Pittsburgh, and lost for the fourth time in five games.

Perdomo walked in the first and Ketel Marte was hit by the next pitch before back-to-back strikeouts of Corbin Carroll and Gabriel Moreno. Perdomo advanced to third on a passed ball by catcher Patrick Bailey and then scored on a throwing error by starter Kai-Wei Teng to make it 1-0.

Casey Schmitt homered in the third to tie it.

Top prospect Bryce Eldridge, a 20-year-old first baseman, made his major league debut for the Giants and finished 0 for 3 with a strikeout. His 407-foot flyout to center field in the seventh would have been a home run in 23 big league ballparks, including Oracle Park in San Francisco.

Carroll doubled leading off the Arizona sixth before Joel Peguero relieved Matt Gage (0-1). Moreno and Blaze Alexander drew back-to-back walks to load the bases for Vargas.

Gallen has 1,005 strikeouts with the Diamondbacks, joining Randy Johnson (2,077) and Brandon Webb (1,065) as the only pitchers in club history with at least 1,000.

The Giants had not announced a starter for Tuesday to face Diamondbacks LHP Eduardo Rodriguez (8-8, 4.98 ERA).

Perdomo and Gallen help surging Diamondbacks inch closer in playoff race with 8-1 win over Giants