Slater had three hits and both RBIs in the Giants' 2-1 victory over Arizona and tough left-hander Patrick Corbin, when the Giants extended their best month since June 2016 while winning for the fifth time in six games and eighth in the last 10.
Slater, in his fourth tour with the team this season, doubled in a run in the second inning for a early lead off Corbin and doubled in the tiebreaking run off left-hander Andrew Chafin in the seventh inning in support of rookie Andrew Suarez and three relievers.
"We're missing a right-handed bat, and he could provide that," manager Bruce Bochy said.
"Not that other guys can't, but you look at what he did tonight and what he's been doing. He's going to help stretch out this lineup and give us some added offense, which we need against lefties."
Slater has been an equal-opportunity attacker this season at Triple-A Sacramento in between his four short promotions to the parent Giants this season, hitting at least .300 against righties and lefties. During his short stay with the Giants before a leg injury last season, Slater hit .333 in 38 plate appearances against lefties.
He is slashing .344/.417/.564 with 24 doubles and five homers in 53 games with the River Cats. Like Friday, his doubles have come in bunches. His 24 doubles were second in the league, and his batting average was sixth when he was promoted again last Saturday.
He went the other way with both of his doubles Friday, lining a ball down the right-field line off Corbin and into the gap in right-center against Chafin.
"That's kind of always been my approach, especially against lefties," said Slater, an eighth-round Draft pick out of Stanford in 2014.
"Both guys had pretty good run and sink to their fastballs, and they actually are both similar pitchers in that they get a lot of chases down and in with their breaking stuff. So for me, it was seeing something up and out over the plate. Had two very hittable fastballs and was able to put it that [other] way and do some damage.
"Just trying to keep the same routine, the same approach" as in Sacramento. "Kind of keep everything as is."
Slater has made three starts since his most recent promotion.
"The first couple of times up and down, it is easy to lose focus," Slater said. "But for me it was try to prove a point that it wasn't a fluke, that I was here to stay."
The outfield is crowded with veterans such as Hunter Pence and Austin Jackson, but playing time will be dispensed according to performance, Bochy said.
"You have to go with the guys who are swinging the bat well," Bochy said.
"They dictate their lineup. [Slater] is a good hitter. The ball jumps off his bat. He uses the whole field well. He's a smart hitter."
MOMENTS THAT MATTERED Suarez used a four-pitch mix effectively, and it helped him get out of jams in the second, third and fifth innings before the D-backs got their one run in the sixth.
With two outs and runners on first and second in the second inning, Suarez got Jeff Mathis to ground into a forceout at third with a 2-2 slider. Suarez got Ketel Marte to ground weakly to shortstop on a 1-0 curveball with the bases loaded to end the third. With two on on and two out in the fifth, David Peralta grounded out on a first-pitch four-seamer.
SOUND SMART Five of the seven hits Suarez gave up did not get out of the infield, barely hard enough to dent grass and rendering his line very deceiving.
Chris Owings' dribbler down the third-base line in the second inning had an exit velocity of 75 mph. Jake Lamb's chopper to shortstop in the second was timed at 76 mph. Peralta's grounder toward the second-base bag in the third registered at 85 mph.
Paul Goldschmidt's single behind second base in the fifth was timed at 84 mph. Owings' grounder in the sixth toward third was clocked at 87 mph.
HE SAID IT "Buster told me my responsibility to the team was to get better, and I took that seriously." -- left-hander Will Smith, who was given that advice after being told that he would need Tommy John surgery in Spring Training of 2017. Smith pitched a 1-2-3 ninth for his first save of the season Friday
UP NEXT The Giants will look to put the finishing touches on their first winning month since June 2016 when right-hander Dereck Rodriguez -- son of Pudge -- takes the mound in the second game of a three-game series in Arizona. The Giants have won four of Rodriguez's first five starts. He gave up one run in a career-high seven innings in a no-decision in his last start Sunday.
Jack Magruder is a contributor to MLB.com based in Phoenix.