The 24-year-old posted a 4-1 record and 2.63 ERA in September, and didn't allow more than three runs in any of his six outings. He allowed just 31 hits and seven walks in 37 2/3 innings, and held opposing batters to a .221 average.
Bonser's September performance was something of a surprise, as the right-hander had struggled throughout the rest of his rookie campaign. He was originally called up from Triple-A Rochester on May 17 to replace Kyle Lohse in the No. 5 spot in the Minnesota rotation, but was sent back down to the Minors on July 5 after he posted a 5.30 ERA in his first seven starts.
When Liriano was scratched from an Aug. 2 start due to a sore left forearm, Bonser was recalled to make the spot start. Teammate Nick Punto noticed the time in Rochester had helped Bonser's attitude about pitching in the Majors.
"It was a huge difference," Punto said. "I think when he got sent down and came back up here, he had a different look and different attitude. The first time, he wasn't real sure of himself, and now he exudes confidence. It just looks like he knows he belongs here."
Bonser was sent down after his spot start, but was back in the Majors for good on Aug. 10 to fill Liriano's spot in the rotation. Liriano's injury woes limited the southpaw to just six innings pitched in August and September, and eventually ended his season.
It was another instance of Bonser's career aligning with that of his more heralded teammate. Bonser and Liriano were both dealt to Minnesota, along with closer Joe Nathan, from San Francisco for catcher A.J. Pierzynski on Nov. 14, 2003.
Now, Bonser joins Liriano as a winner of the Rookie of the Month Award. Liriano took the honors in both June and July.
Of all of Bonser's strong outings in September, none was bigger than his Sept. 9 start against Detroit. With the Twins and Tigers locked in a struggle for AL Central crown, Bonser held Detroit to one run on five hits in seven innings as Minnesota picked up an important 2-1 win.
"He gave them a variety of pitches and attacked them," said Twins manager Ron Gardenhire after the game. "I mean, he just kept coming at them and never quit. When he had to make some really big pitches, he made them. He did what he had to do."
Bonser also played the key role in the game that put the Twins in the playoffs. He held the Royals to two hits in 6 2/3 innings on Sept. 25 to lead Minnesota to an 8-1 win that clinched a playoff spot.
The next step for Bonser in his wild rookie campaign is his first career postseason start. He is scheduled to start Game 2 of the American League Division Series on Wednesday, when the Twins host the Athletics.
"I've never been in that playoff spot, but I'm hoping to find out what that is here soon," Bonser said.
Other rookies who received votes were Angels pitcher Joe Saunders (3-1, 4.64 ERA, 25 strikeouts), Royals first baseman Ryan Shealy (.253 average, four home runs, 18 RBIs) and Indians first baseman Ryan Garko (.271, three home runs, 25 RBIs).