How long can Dodgers continue with black hole in back of rotation?

Once more into the breach, dear friends, once more.

Exactly how many more, however, is a growing question. And for many, a question of growing concern.

The back end of the Dodgers’ rotation continues to be a problem. And it might not matter how good their front three starters are, if the back two can’t help get them into the postseason.

Josh Beckett suffered another rough and short outing Sunday, coming on the heels of another trying start from Dan Haren. Both are veteran right-handers used to success, both searching for answers with less than a third of the season remaining.

Beckett lasted only four innings Sunday, and needed 94 pitches (only 53 strikes) to do that. He struck out four consecutive Cubs at one point, but also gave up three runs, six hits and three walks.

In three starts since coming off the disabled list, where he spent two weeks because of a sore hip, Beckett has failed to pitch out of the fifth inning. And his latest effort came after a 12-inning game Saturday that spent the bullpen.

“Three starts in a row like that, it’s a pretty helpless feeling,” Beckett said.

“I felt better physically today than I have in my last couple starts. But the results were still the same. … I need to get ahead. I need to attack better. I need to do a better job of putting guys away.

“I didn’t throw enough strikes today and the strikes I did throw weren’t quality.”

The Dodgers have little choice but to be patient with Beckett and Haren. They have no other options on the team, and no one in the system whose pitching is demanding a call-up.

A trade for a waived player is a growing possibility. They can’t keep starting Beckett and Haren every fifth day and have their bullpen destroyed. They might have to at least try someone.

“Well, I’m sure that’s up for discussion with Ned [Colletti] and his guys,” Manager Don Mattingly said. “We’ll always be trying to get better. But Gonzo [Adrian Gonzalez] struggled before the break and we didn’t do anything with him.

“We think guys are going to come out of those things, they’re not going to continue to struggle. At some point I guess you continue to look, but from my standpoint and the coaches’ standpoint, you think guys are going to get better and improve, and the next outing is going to be better. That’s why you don’t just make changes all the time.”

At least one of the two will need to find his form. Both had their share of early success -- Haren started 5-1 with a 2.84 ERA, Beckett had a 2.02 ERA through 15 starts -- but neither are exactly young. Beckett is 34 and Haren turns 34 next month.

This is Beckett’s 14th season in the majors and he has more than 2,000 innings in his career. He no longer throws bullpen sessions between starts.

“I’m old. It’s just where I’m at,” Beckett said. “I can’t force myself to go out there two days after I pitch. I feel like it’s robbing Peter to pay Paul if I try to throw a bullpen.”

The Dodgers will need to rob their system or another team’s roster soon if the back end of the rotation doesn’t settle down soon.