In the four games, starters Drew Pomeranz, Chris Sale, Rick Porcello and Eduardo Rodriguez have logged an aggregate 14 1/3 innings while giving up 20 earned runs.
Rodriguez was on the hook for Thursday's 12-2 loss to the Astros, getting drilled for five runs over just 1 2/3 innings.
The late-season slump by the rotation is happening at the same time manager John Farrell is trying to plot his plans for a potential AL Division Series presented by Doosan against the Astros or Indians.
If the Red Sox do what is likely and win the AL East, the only near certainty is that Sale would pitch Game 1 next Thursday.
Pomeranz is the front-runner for Game 2, but his start Monday night (two innings, five runs) was his shakiest in months and his velocity was down.
Before Thursday's mishap, Rodriguez had built momentum to pitch Game 3 with four solid starts in a row.
"We just have to keep working on it over the next three games and see who's going to start in the postseason," said Rodriguez. "And whoever it is, just do their job."
Doug Fister, who gets the nod on Friday, was on a strong roll a couple of weeks ago. Then he went into a three-start slump before having a decent performance last time out.
Then there is Porcello, who has been an enigma (11-17, 4.65 ERA) in the season after winning the AL Cy Young Award but joins Sale as the only pitchers on the staff to top 200 innings.
"I think this turn through the rotation starts to make you think about how our pitching staff is best comprised," said Farrell. "Is there length needed from a couple of [relievers]? All those things are being brought into the mix. We recognize where guys are in terms of workloads, the way they've thrown of late, early exits. Yeah, that kind of starts to factor in, and are there multiple-inning guys needed more than one-inning guys? All those are all things we'll take into account."
What has happened of late to a rotation that has, by and large, been a strength for most of the season?
"Any time you go through spells or turns like this, it comes down to consistent location and command," said Farrell. "There's not a magic elixir to this. It's a matter of going out and executing pitches."
If the Red Sox do wind up playing the Astros in the ALDS, they hope Houston cools off at least a little at the plate.
"They're hot," said Red Sox pitching coach Carl Willis. "They're swinging the bats and that's great. But our pitchers getting a little bit of a blow will help. And their guys aren't going to get any live at-bats for three days."
This Red Sox-Astros series to close out the regular season has brought back some memories for Willis. In 1991, he was a reliever on the Minnesota Twins, who lost two of three to the Blue Jays to close out the regular season but then beat Toronto in the AL Championship Series before winning the World Series.
"They pretty much handed it to us the whole year-round, and we had to turn around and play them in the ALCS," said Willis. "We were able to turn the tables. Once the postseason starts, it's a new season. We just have to go and execute the things that helped us get here."
"We've got to lead the way from the mound," said Farrell.