PHOENIX -- Cal Quantrill is starting to face some adversity as he nears the completion of his rookie season. The 24-year-old right-hander is confident it won’t last for long.

For the second straight start, Quantrill allowed eight runs, and the Padres dropped their series opener Monday afternoon vs. the D-backs, 14-7, at Chase Field. Quantrill, who had a 1.79 ERA in his first seven games (six starts) after the All-Star break, has allowed 16 runs over his last 9 1/3 innings.

Most of the D-backs’ damage against Quantrill came in the second inning, when he allowed six runs on five hits. He gave up three consecutive singles to open the frame and later allowed an RBI double by Josh Rojas and a two-run homer by Ketel Marte.

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“You’ve got to control innings. You can’t have an inning get away from you like that,” Quantrill said. “It just puts your team in too bad of a spot. I know I’m capable of competing here. I know I’m capable of dominating. Right now, I’m not doing it.”

In the third, Quantrill escaped a jam that was started by an error from shortstop Luis Urias. He got D-backs starter Mike Leake to ground out to strand a pair of baserunners. Then, Quantrill retired the side in order in the fourth.

Quantrill completed five innings, although he gave up a two-out, two-run double to Alex Avila in his final frame.

The right-hander had a 3.32 ERA entering his previous start against the Dodgers, but that mark is now up to 4.57 after his tough two outings against National League West rivals. Padres manager Andy Green believes this one could have taken a different direction had Quantrill limited the damage in the second.

“That six-spot changes things drastically,” Green said. “He wasn’t able to make those pitches at that point in time, and the contact got a little louder throughout the rest of that inning. … There are still some pitches that he knows he can execute better than that.”

In the sixth, Quantrill was replaced by right-hander Javy Guerra, who made his MLB pitching debut after getting called up from Double-A Amarillo when rosters expanded Sunday. After playing 13 big league games as an infielder last season, the 23-year-old was converted to a reliever this year.

It was a tough first showing for Guerra as he allowed four runs on five hits, including a trio of home runs, in two-thirds of an inning.

“He hasn’t pitched a ton,” Green said. “Those are situations early on that we’re going to find him in, those types of situations to give him some opportunity at the big league level. It’s a live fastball. He got his first punchout, but he spun a couple sliders in the middle of the plate that didn’t have depth and bite to them, and they got hit really far.”

Three of the Padres’ runs came on one swing from red-hot Ty France, who went deep in a four-run sixth. After hitting two homers in his first 48 big league games, the rookie infielder has three in the past two games.

During the final month of the season, San Diego will continue to evaluate young players, such as Quantrill, Guerra and France, as it gives them a chance to adjust to the Majors.

For Quantrill, the recent growing pains haven’t been fun. But he knows they won’t last forever.

“Good pitchers adjust faster than bad pitchers. Right now, I’m adjusting far too slow, and they made me pay for it,” Quantrill said. “My arm feels good. I’m going to get it, I’m going to throw the ball correctly. Just right now, I’m not doing it. It’s disappointing. It sucks sucking, and it sucks not giving your team a chance to win, but it’s part of the game and I will be better next time.”