Kelly couldn't get out of the second inning, as the Twins came up with six runs in the frame.
"The attitude, the feel, the energy level in the clubhouse this morning was built upon the last two days, and to go out and to have a game like today is very disappointing," said Red Sox manager John Farrell.
Typically in baseball, momentum is only as good as the next day's starting pitcher.
Over Kelly's two previous outings, he had allowed just three runs over 13 1/3 innings.
In this one, the Twins pounded him for eight hits and seven runs over 1 2/3 innings.
"It's not ideal, but I've just got to keep pitching," said Kelly.
What was the biggest problem Monday?
"You know, a number of pitches found their way to the middle of the plate and whether it was hard contact or soft contact, [there were] a high number of base hits," said Farrell. "They put up six in the [second] inning and you've got to go to the bullpen at that point in that second inning. A short day and unfortunately we get a hole dug pretty darn deep here today."
In the big picture, Kelly is 1-4 with a 6.24 ERA. Farrell didn't sound ready to take him out of the rotation.
"There's no decision here in this moment," Farrell said. "He's shown us the ability to go out and work deep in a ballgame. There's no denying the stuff. It's a matter of consistent location with his fastball. When he's in those games where the runs have come about, it's typically been mislocated fastballs that found their way to the plate."
After showing a decent revival offensively Saturday and Sunday at Fenway, the Red Sox were stifled by Ricky Nolasco, who at one point retired 15 in a row.
Of course, Nolasco had the advantage of pitching with a big lead for nearly the entirety of his outing.
"They came out swinging, real hot," said Kelly. "They've done that the past few games. I knew they were going to come out swinging. They were right on the heater every time, put some good swings on some balls, got on base and created me pitching from the stretch and scored some runs that way."
Kelly will try to get right again for his next start Saturday at Texas.
"You take stuff from every little game. I'll go back and watch the game, probably [Tuesday], and see where I went wrong and try to build on that," Kelly said.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.