PHOENIX -- What started with the Padres presumed to be a candidate for the top spot in the National League West when the season began has morphed into an intense competition for one of the league's Wild Card spots.

Defeats, then, especially during the final months of the season against teams they are supposed to beat, can be troublesome to the Padres. Thursday’s 12-3 loss to the D-backs at Chase Field hurt in more ways than one.

Padres starter Yu Darvish was escorted off the field by head athletic trainer Mark Rogow with what the team called lower back tightness after a short outing against the D-backs. The right-hander was tagged for five runs on six hits in 2 2/3 innings, logging 74 pitches in the brief appearance.

“He did mention that, for whatever reason, he's dealt with the lower back issue or tightness here [at Chase Field] in the past,” Padres manager Jayce Tingler said. "I think it was both with Chicago and the Dodgers in the past. I don't know exactly why. You wouldn't think that playing catch on the turf or doing anything there [would be a factor] but for whatever reason, he said he's had that issue here in the past.”

How long Darvish will be out of action and whether he will land on the injured list has yet to be determined. The Padres will get more clarity on his status in the coming days. But with Chris Paddack (left oblique strain) on the injured list and Ryan Weathers struggling to find his form, the Padres can’t afford to have Darvish miss a start. The club is already considering using career-reliever Craig Stammen, who threw 11 pitches in an appearance on Thursday, in the rotation. Friday’s starter Blake Snell has been inconsistent for most of the season.

With the loss, the Padres, who have lost two in a row, lead the Reds by 3 1/2 games for the final Wild Card spot. Darvish, the staff ace, is presumably the favorite to start the aforementioned Wild Card Game -- if the Padres can hold off Cincinnati for the final seven weeks.

But no matter what, the Padres need Darvish to be strong down the stretch. He spent time on the injured list last month and struggled for most of July, but he appeared to be completely healthy to start August. The veteran struck out 12 in a solid seven-inning outing against the D-backs in his previous start last Saturday.

Darvish was back -- or so it seemed -- and he took the mound at Chase Field seeking another solid performance. What he received was his shortest outing of the season and a painful reminder of how quickly fortunes can turn. He wasn’t sharp, missing location on a few key hits in the D-backs' five-run third inning and appearing restless on the mound, occasionally bending at the waist and trying to stretch his legs.

“He just said it kept getting tighter and tighter as it went on the third,” Tingler said. “When I went out there, that’s what he was saying. He said on both sides.”

Darvish’s absence put the bullpen in action. In all, the Padres used six pitchers in the loss. 

“Obviously, like I said, it’s frustrating tonight and certainly a gut punch,” Tingler said. “But at the same time, it's still early. It's not like Darvish is done for the year or anything like that. We'll see how he responds and go from there.”