Diamond's rookie campaign was even more impressive considering he was a long shot to make the rotation out of Spring Training and was sent to Triple-A Rochester in the first round of cuts in mid-March.
But Diamond excelled in Rochester and ended up being called up for good in early May, as the 26-year-old became the club's most dependable starter the rest of the season.
Among AL rookie starters, Diamond tied for fourth in wins (12), third in ERA (3.54), sixth in innings pitched (173) and ninth in strikeouts (90).
As a result, he's the lone Twins starter guaranteed a spot in the rotation next year, as Twins manager Ron Gardenhire gave him the nod of approval at the end of the season.
"I would say that without even thinking about it," Gardenhire said. "He's definitely one of the guys we count on for next year."
Diamond's 2012 season came as somewhat of a surprise for the Twins, especially as he posted a 5.08 ERA in seven big league starts in '11 and wasn't any better at Triple-A with a 5.56 ERA in 23 starts.
But the club liked what it saw in Diamond despite those numbers, considering the Twins took him from the Braves in the Rule 5 Draft before the season and were able to keep him by sending pitching prospect Billy Bullock to Atlanta.
The decision to take Diamond in the Rule 5 Draft -- the same way the Twins acquired former ace Johan Santana before the 2000 season -- paid off in 2012, as the left-hander put it together at both Triple-A and in the Majors.
He also proved to be a workhorse, throwing a combined 207 2/3 innings between Rochester and Minnesota to reach the 200-inning mark for the first time in his career.
Diamond, who made his last start of the year in his native Canada against the Blue Jays, said he was proud to cross that threshold and was happy with his rookie season despite the club finishing with the worst record in the AL for the second straight year.
"Personally I'm pretty happy, but as a team we didn't do too well," Diamond said. "So I'm going to look to improve on some things for next year, maybe some repertoire stuff. But for the most part, I'm going to try to contribute the same way I did this year."
Diamond was able to find success despite not having an overpowering fastball, as it averaged just 89.4 mph, according to FanGraphs.com.
But with his over-the-top delivery, he used deception to his advantage and was adept at getting ground balls.
He was also big on using video to his advantage, as he spent a lot of time before his starts analyzing opposing hitters and their tendencies.
"He was a real bright spot for us this year, taking the ball every fifth day," Twins catcher Joe Mauer said. "He has a pretty good idea. He definitely does a lot of work studying film and studying the other hitters, and kind of one of the more in-depth conversations when we go over a lineup that next day. So that's real good that he pays attention to those things and he wants to learn."
So it was an impressive rookie year to say the least for Diamond, and given their pitching problems the last few years, the Twins are hoping he can build on it to become a fixture in the rotation for years to come.