"I was able to end on a good note, which was a definitely a positive," Collmenter said. "From last year and being able to take it in, it will be positive from this year and taking it into next year as well."
Collmenter was a surprise a year ago, starting the season in the bullpen before moving into the starting rotation and posting a 10-10 record and 3.38 ERA.
Expectations were high for his second season but he floundered from the start. In his first four outings, Collmenter allowed 20 runs on 25 hits in only 18 1-3 innings and was demoted to the bullpen.
And in making the change, the season turned around. Collmenter allowed only three runs in his first nine relief outings spanning 18 2/3 innings and made a spot start June 22. He bounced up and back between the rotation and the bullpen before ending the season with consecutive one-run, five-inning starts.
He finished with 11 starts, 17 relief appearances and a 3.80 ERA after allowing only 17 earned runs after those first four starts.
"It started off pretty terrible," Collmenter said. "Then I got into a groove in the bullpen and got back to what I do well and was able to get some spot starts. I know what I do well and how I can get guys out. Once I got back to doing what I do the best and was throwing strikes down in the zone, it was good."
Collmenter turned a 2-1 lead over the Diamondbacks bullpen in the sixth, but it didn't last long.
Anthony Rizzo and Alfonso Soriano singled with one out in the sixth against Bryan Shaw (1-6).
Starlin Castro was safe when first baseman Mike Jacobs couldn't pick up his grounder down the line, and the error loaded the bases.
After Mike Zagurski struck out Luis Valbuena, Matt Albers relieved. Pinch hitter Dave Sappelt hit a grounder that Jacobs scooped, but the throw to Albers covering first base was a half-second late. Sappelt's infield hit made it 2-all.
Albers then hit Anthony Recker with a pitch to force home the go-ahead run, and Bryan LaHair followed with a single to right to make it 5-2.
The Cubs added an unearned run in the seventh on a three-base throwing error by Brad Bergesen, the Diamondbacks' fifth of seven pitchers, and another error two batters later by third baseman Cody Ransom.
DeJesus homered to right off Takashi Saito in the ninth for the Cubs' final run.
"We gave up seven runs and three of them were earned," said D-backs manager Kirk Gibson. "That's pretty tough. We can be frustrated but the reality of it is they had three earned runs out of seven. It wasn't a very clean game from the seventh inning on."
Rizzo had three hits as the Cubs snapped a seven-game losing streak overall and a 19-game losing streak against the NL West dating back to the final game of last season. The win was Chicago's second in its past 13 games overall.
"If we're going to win one, it might as well be the last one on the west coast," said Cubs manager Dale Sveum. "It wasn't the prettiest thing ever."
Chris Rusin (2-3) scattered three hits, allowing two runs -- one earned -- with two walks and four strikeouts for his first win since September 14 against Pittsburgh.
Rizzo doubled home DeJesus in the first against Collmenter for a 1-0 lead.
The Diamondbacks scored twice in the bottom half. Ransom drove in a run with an infield single, and another scored on Recker's error for dropping Rusin's throw home for a would-be force out.
Collmenter went five innings, allowing a run on six hits with two strikeouts.
"I thought we would be able to get to their guy, but they did a good job from the first inning on," Collmenter said.
The Cubs, sitting on 99 losses, need to sweep their three-game home series against the Astros to avoid losing 100 games for the first time since 1966.
NOTES: SS Starlin Castro came up limping after turning a double play in the eighth but remained in the game. ...
Aaron Hill went 1 for 3 to move into fifth place on the Diamondbacks' single-season hits list with 180. ... Cubs 2B Darwin Barney, whose 141-game errorless streak was snapped on Friday, returned to the lineup after an off day on Saturday. ... D-backs 1B
Paul Goldschmidt missed his third straight game with a sore back. ... RHP Jason Berken (0-2) will be the next to try and keep the Cubs from their 100th loss when he takes the mound Monday night against RHP Lucas Harrell (10-11). Berken will be making his fourth start since he was claimed off waivers from Baltimore on Sept. 7. ... D-backs LHP Wade Miley (16-11) will face Rockies LHP Drew Pomeranz (1-9) on Monday. Miley is tied with Jason Jennings, the 2002 NL Rookie of the Year, for the most wins by an NL rookie since 1986.