SAN DIEGO -- It’s still May, so it’s far too early to start talking about magic numbers in the traditional sense. But the D-backs do have a magic number of another kind.

Four.

If the D-backs score four runs, they’re probably going to win. If they don’t, they probably won’t.

It was a “won’t” kind of night on Monday as the D-backs faced rookie sensation Chris Paddack and then squandered their best opportunity against the Padres’ bullpen in a 2-1 loss at Petco Park.

• Box score

The D-backs fell to 6-14 when they score fewer than four runs. They’re 19-9 when they score at least four.

“We only scored one run, and that’s really the name of the game,” manager Torey Lovullo said.

The lone run wasn’t enough cushion for D-backs starter Luke Weaver to survive his only slipup of the evening. Nearly untouchable the first two trips through the Padres’ lineup, Weaver allowed three straight hard hits by the first three batters to see him a third time. The one that proved decisive was a 422-foot, two-run blast to center field by Franmil Reyes, who attacked a first-pitch cut fastball to the tune of a 110.3 mph exit velocity.

“That one just hurts,” said Weaver, who retired 17 of the first 18 batters he faced.

Austin Hedges singled in the third. In completing that inning while throwing from the stretch, Weaver (3-3) felt a bit out of sorts. His pitches were running a bit on his arm side.

He got through that inning and didn’t have a baserunner aboard again until Greg Garcia singled ahead of Reyes’ at-bat in the sixth. Weaver had doubts that a cut fastball was the way to go because he didn’t have great feel out of the stretch three innings prior.

“Hindsight’s 20-20. But in that pitch, it just wasn’t the right call and I kind of felt that before I threw it,” Weaver said. “It’s a mental error, and I just need to step off and gather. I need to think about it or just throw something else.

“It just spun out of my hand. Good hitter. Power hitter. He put a good swing on it.”

The D-backs’ best chance to get the lead back came in the top of the seventh, with Paddack having departed for a pinch-hitter a half-inning earlier. With one out, relievers Trey Wingenter and Adam Warren threw 12 straight balls to walk the bases loaded with the top of the order coming up. But Warren bowed his neck and struck out Jarrod Dyson and induced an inning-ending grounder to first from Ketel Marte.

“I thought we had built that inning exactly the way we hoped,” Lovullo said. “Jarrod, the right guy. He has a tremendous knowledge of the strike zone, knows how to execute in crucial situations. Unfortunately, we didn’t get it done.”

The D-backs’ run off Paddack came in the third inning, when they collected three singles -- none of them particularly hard-hit. Dyson got the RBI on fielder's choice ground ball to second.

The D-backs rank second in the National League with 242 runs scored, but they are trending in the wrong direction. Since their apex of 20-13 on May 4, they have gone 5-10 and scored fewer than that magic four runs nine times.

“Getting runs is hard,” Weaver said. “Sometimes it takes one swing. Sometimes it takes a rally. But getting wins and getting runs across is tough in this league, especially when you have opponents who are throwing it well.

“You could see tonight, it’s just tough to do. It doesn’t mean that we’re not going to get the bats going and crush it. Because we’re a great team. When we get hot, we get hot.”