Doug Fister, who had gone 5-2 with a 2.79 ERA in his first seven starts since replacing David Price in the starting rotation, was hit hard.
The righty gave up six hits and six runs over just four innings, walking one and striking out four.
The subpar outing could cool some of the recent speculation of Fister being the No. 3 starter going into the postseason behind Chris Sale and Drew Pomeranz.
And a troubling trend continued for Fister, as he was scored on in the first inning for the fifth straight start. In the postseason, when every inning is so crucial, the last thing the Red Sox will want is to have an early deficit.
"I have nothing to explain it. I really have no idea," said Fister. "I got out there with the same mentality, same approach first inning, last inning, it doesn't matter. It's one of those things, I guess. I need to start kicking myself in the shin and be ready in the bullpen, just kind of get mad from the get-go. I've got to figure that out myself."
Meanwhile, Eduardo Rodriguez, who was looking like the odd man out less than two weeks ago, is starting to heat up. The lefty was powerful in Tuesday's win, giving up a run over six innings while striking out nine.
In his last two starts, Rodriguez has given up three runs in 12 innings and has looked more like the pitcher who thrived in the first two months of the season before re-injuring his right knee.
Then there is Rick Porcello, who has fallen sharply since being handed the honor of pitching Opening Day after an AL Cy Young Award season in 2016.
Porcello is 9-17 with a 4.64 ERA and has allowed 35 home runs. The righty would need to finish strong to be assured of a start in October.
Price likely doesn't have enough time to re-emerge as a starter this season. Instead, he could turn into a multi-inning weapon out of the bullpen in the postseason.
Depending on how a potential Division Series evolves, Red Sox manager John Farrell could deploy either three or four starters in a best-of-five series.
Of the three starters who are jockeying for position, Rodriguez has the best pure stuff. But he is also prone to inconsistency and is 24 years old with no previous experience in the postseason.
Fister offers a history of playoff success, going 4-1 with a 1.78 ERA in eight starts. He also has the most compelling storyline, given that he didn't have a job when the season started and the Red Sox got him off waivers from the Angels in June.
As rough as things have been for Porcello at times this season, he's second on the team to Sale in quality starts (18) and innings (186 1/3).
All three pitchers will get multiple opportunities to make their case over the final 17 games.