The 27-year-old, who is out of options, bounced back from a pair of rough outings to allow two runs on three hits over 3 2/3 innings in a 3-3 tie.
Six of his 11 outs were via the strikeout, all of which were swinging. He issued three walks.
"I thought today was a big day," said Diamond, who threw 64 pitches (38 strikes). "If I didn't show some progress or some steps toward getting back to my former self, I think it was going to be a real tough stretch. Today, even with the walks, I felt my timing was better, my rhythm was a lot better [and] my pace was a lot better. I'm happy with how the outcome was."
In his past two appearances, Diamond had allowed seven runs (three earned) on eight hits and three walks over four innings.
Not only was his fastball command better on Saturday, but so were his secondary pitches. Diamond credits guys in the locker room for noticing some things to tweak. For one, he stayed on his back side a lot more, which improved the direction of the ball.
"Curveball was really working well for me today," said Diamond, whose ERA dropped from 6.00 to 5.59. "I think that's a really good sign, given that it's probably been the last pitch to come back since 2012."
Twins manager Ron Gardenhire has said he wanted to see the pitcher who posted a 3.54 ERA in 27 starts as a rookie in '12. Last season, he began the year on the disabled list because of offseason elbow surgery. Upon his return, he finished with a 5.43 ERA in 24 starts.
Though he did not pitch a clean inning, Diamond didn't labor much.
Chris Young blasted a solo home run deep to left with two outs in the first. In the third, Matt Reynolds led off with an infield single and moved to third on Matt den Dekker's sharp single to right. Reynolds scored on Daniel Murphy's sacrifice fly.
Righty Anthony Swarzak came on in relief with a runner on second with two outs in the fourth following Diamond's wild pitch on a strikeout of Taylor Teagarden.
"Diamond's first inning was so-so, but after that he threw the ball well," Gardenhire said. "The ball came out of his hand good. Too many walks -- he knows that -- but overall a good performance for him. Throwing the ball well, had some dive to it, his fastball had some movement."
Added Diamond: "It was a step in the right direction. We'll just continue to work on it for that next start. Whether there will be a start or coming out of the 'pen again, I'll prepare the same, because you've still got to get that pitch count up."