PHOENIX (AP) — Tyler Skaggs' inexperience was on display Friday night.
"He is very young," Arizona manager Kirk Gibson said after the left-hander lasted just four innings in a 6-2 loss to the San Francisco Giants. "You look at all the 21-year-olds who have been in the game over the history of the game, they learn a lot of lessons. It is painful and tough for him."
Skaggs (1-2) allowed five runs and five hits after lasting only three innings in his previous start against San Diego on Sept. 7. He also failed to cover first on a ground ball that took an odd hop off the edge of the first-base bag in the second, though the miscue didn't come back to hurt him.
"That was just a mental error," Gibson said. "He's young. He thought the ball was going to go foul and he didn't get over there. He will learn from that. The result isn't what he wants it to be but your hope is he will have the character to make him better. If we didn't believe that, I don't think he would be here."
Skaggs retired the side in the first and fourth but gave up five runs in the third, the bulk coming on Hunter Pence's third career grand slam.
"It's been unacceptable on my part the last two outings," Skaggs said. "It's almost been embarrassing. As a young pitcher you have to learn to get out of jams like that. I was fortunate my first two outings to get out of jams."
Pitcher Matt Cain sparked the outburst in the third with a leadoff walk and moved to second on Marco Scutaro's one-out infield single. After Pablo Sandoval singled to center to load the bases, Buster Posey hit a grounder to third and Cain slid under Ryan Wheeler's throw on a close play to make it 1-0.
Pence followed with a long drive into the left-field stands for his fourth homer since he was acquired from Philadelphia at the trade deadline. It was No. 21 overall for the season.
"You can never walk the pitcher," Skaggs said. "I thought they were good pitches but I ended up walking him and then the whole inning kind of exploded."
Chris Johnson drove in both runs for the Diamondbacks, who stayed 4½ games behind the Cardinals for the NL's second wild-card spot.
Arizona left 15 men on base against seven Giants pitchers.
Cain (14-5) walked three in the first and stranded five runners over the first two innings.
The right-hander allowed four hits, walked a season-high five and also hit a batter over five-plus innings. He was charged with one run and struck out two.