Of his 10 starts this season, Buchholz only performed well on two occasions. Overall, he is 2-5 with a 6.35 ERA. He has given up five runs or more in six starts.
The move to the 'pen came a day after Buchholz was tagged for six runs and a trifecta of two-run homers in an 8-2 loss to the Rockies.
"The bottom line is the results, and there's been a strong precedent set with that," said Farrell. "I can tell you that Clay understands the decision but probably doesn't like it, which I can respect, but at the same time, the most important thing as we stand today is how he embraces this decision, how this change will work itself out."
Buchholz declined to speak to reporters before Friday's game.
"His attitude toward the move has got to be one where you take this as an opportunity to work through some of the issues that have presented themselves, and that's been the big innings or that's been the home runs that have come with men on," said Farrell. "Maybe in shorter stints, shorter looks, he begins to gain a little momentum and gets back on track."
Of Buchholz's 179 career appearances, only two have been as a reliever. Buchholz last pitched out of the bullpen on Aug. 17, 2008.
"This will be an adjustment for all of us," said Farrell. "How Clay goes through a warmup routine will be adjusted. He won't have the benefit of long toss as a starter does. We'll see him as a multi-inning guy initially until we get some repetition and appearances out of the bullpen. That's the plan right now."
Buchholz likely won't be ready to pitch in relief until early next week as he goes through his normal post-start recovery.
"He's been a good Major League starter for a good number of years now, and this is certainly going to be different," said Red Sox pitching coach Carl Willis. "I think in the first few days, mentally it's going to be an adjustment for him as well. Hey, no one is more disappointed than he is as far as performance goes. His attitude has been good as far as how he's going about working and trying to correct it and get better.
"Obviously he won't be available for us to pitch out of the bullpen for a few days. It will give him time to let this resonate a little bit and settle in. I think we'll see Clay Buchholz back and successful again and fare well as a starter."
There are no physical issues with Buchholz, and no detectable flaws in his mechanics, and that combination has made his struggles all the more perplexing.
"When you look at the raw stuff, if you grade out the pitches, it probably is better than any point last year -- and yet there's been missed location, and he's in a stretch where seemingly when mistakes are made, it's resulted in a ball that's been squared up," said Farrell. "It's a matter of more consistent execution which ultimately has not been there when you look at the big innings."
Farrell will do his best to keep Buchholz stretched out so he can move back to the rotation in short order if the opportunity presents itself.
"We're in May. For us to say that on May 27, the five guys that would be in the rotation will make every start for the remainder of the year is probably a little aggressive," said Farrell. "In our conversation and sit-down, I mentioned to him that his starting days may not be over. For the time being, this is the approach we're taking."
This is Buchholz's 10th season in the Major Leagues, and he's spent his entire career with the Red Sox, who hold a $13.5 million option on him for 2017.
Rodriguez is coming off a patella subluxation in his right knee that he suffered on Feb. 27. In his rookie season last year, Rodriguez went 10-6 with a 3.85 ERA.
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.