Things were moving along well for the D-backs through the first three innings Monday afternoon at Petco Park.

The offense had taken advantage of a pair of Padres miscues to take a one-run lead, and starter Luke Weaver was keeping San Diego’s bats in check.

That all changed quickly in the fourth, as the first six Padres reached base and blitzed Weaver for five runs on their way to a 6-2 win. San Diego took three of four from Arizona in the season-opening series.

• Box score

Weaver was charged with six runs on seven hits as he lasted just 3 1/3 innings, the third D-backs starter of the series who was unable to get through five innings.

“It ended up being an abomination,” Weaver said. “Everything felt fine. The inning just kind of got away from me, and it happens fast, especially at this level. And I’ve just got to learn from it. I know the things I need to work on and be more efficient next time.”

There were a lot of takeaways from this series with the Padres. Here’s a look at three of them:

1. The starters need to pitch deeper into games
Aside from Madison Bumgarner on Opening Day, no starter made it past the fifth inning, and the only one to come close was Zac Gallen, who lasted four on Sunday.

The D-backs pride themselves on their starting pitching, or as manager Torey Lovullo likes to say, “We’re built around our starters,” and a big key to that is their ability to give the team some innings.

“I know for myself, I’ve got to step it up,” Weaver said. “And I think as a staff in general, you know we talk and we know that there is a huge sense of urgency. We've got to be efficient, we’ve got to make sure that we're letting our defense work, because we’ve got a pretty stinking good one.”

The key to being able to pitch deeper is to have fewer deep counts, and in order to do that, the starters must be more aggressive early in them.

“Strike 1,” Lovullo said. “Strike 1, put the ball on the plate, trusting their stuff.”

2. The offense can learn from the Padres
Padres hitters constantly worked deep counts, racking up 28 of them in the first two games of the series, and they simply grinded down the D-backs' pitchers.

On the flip side, the D-backs seemed a little too aggressive on offense, allowing the Padres’ arms to have low-pitch-count innings.

“I think there was just anxiousness,” Lovullo said. “Especially in the first couple of games where we were trying to do pull-side damage on every pitch. You know, to me, the art of hitting is setting up the pitcher, waiting for a mistake, using the whole field. And we’ve got good hitters. So those are reminders to make sure we’re [working] the counts, having smart at-bats and controlling the at-bats.”

The D-backs showed that kind of grind-it-out approach against Padres closer Kirby Yates in their Sunday win, scoring a pair of ninth-inning runs by laying off pitches just off the plate and making the right-hander come into the zone with his offerings.

“Maybe a little bit of trying too hard,” shortstop Nick Ahmed said. “You know guys are going to get their timing, myself included, and the bats are going to wake up and we're going to start swinging better.”

3. The pitching depth looks good so far
There was some concern -- particularly after the way Taylor Widener and Taylor Clarke were roughed up by the Dodgers in an exhibition series last week -- that maybe the team’s starting-pitching depth was not as strong as advertised.

That may have been a bit premature.

Alex Young -- who lost out on the fifth spot in the rotation -- delivered two scoreless innings on Sunday, Widener had 1 2/3 scoreless frames on Saturday and Clarke worked 3 2/3 scoreless frames on Monday.

Depth is important this season, and to have it on the mound is even more so.

“I loved that,” Lovullo said of the trio’s performance. “Very encouraged by that. We know what they're capable of, and getting their opportunity I know was exciting for them. But going out and executing a good plan was probably an even better feeling.”

Up next
The D-backs travel to Arlington on Tuesday, when they will open a two-game set with the Rangers at 6:05 p.m. MST, live on MLB.TV. Merrill Kelly will make his first start of the year for Arizona after winning the No. 5 spot in the rotation with a strong showing during Summer Camp. Kelly made 32 starts last year for the D-backs, second to Robbie Ray’s 33, after spending the previous four seasons pitching in Korea.