With four games remaining in the regular season, Arizona needs one more victory to secure at least a .500 record this year. The club saw its slim National League Wild Card hopes end on Friday when the Cardinals won in St. Louis.
"I just wanted to come in, have a good start, and give the team a chance to win," Cahill said. "The offense got on them early, so I got to pound the zone."
Cahill's stellar outing Saturday put the finishing touches on an impressive final month of the season after the 24-year-old went winless in August. In 34 1/3 September innings, the right-hander surrendered 10 earned runs while striking out 31 and recording a 4-1 record.
"It's just momentum into next year," Cahill said. "It'll give me a good mindset going into the offseason."
The complete game gave Cahill exactly 200 innings pitched in 2012, the second time he has reached the mark in his career.
"It's a big number, to get there is sweet," he said. "I was always told that 200 is a goal."
As the night progressed, D-backs manager Kirk Gibson and the rest of Cahill's teammates all knew he needed to finish the game to secure the milestone, providing extra motivation for the club to help him out in any way possible.
"He seemed kind of determined," Gibson said of Cahill. "We got him a lead and he settled in. We wanted to let him get his nine innings in, we knew he had 191 coming in. He's really pitched better and pitched well for us this year."
The right-hander was two outs away from tossing a complete game shutout, but Cubs outfielder Alfonso Soriano spoiled the night with a two-run homer to center field in the ninth inning.
"I was trying to throw one off the plate so he would ground out, get a double play and end it," Cahill said. "But it stayed up high, and he's a good player."
Soriano's long ball came on an 0-2 pitch up in the zone after Cahill walked Anthony Rizzo earlier in the frame.
"The ball moved so much, and he had very good command today, and a heavy sinker, good slider, good changeup," Soriano said. "He threw a very good game today. You have to give a lot of credit to him. He knows what he's doing on the mound."
Perhaps even more locked in than his pitcher in September, Upton collected two hits on Saturday, including his 17th home run of the season on a second-deck shot to left field.
In 99 at-bats this month, Upton has a .303 average with six long balls, 14 RBIs and 22 runs scored. Prior to September, the 25-year-old hadn't hit more than three homers in a single month this year.
"He told me he was going to try to go 'oppo,'" Gibson said. "Then the next time he told me he's going to crank it, and I said 'Oh, that's never good.' But he sat on it, put a good swing on it, and let it travel."
The lineup provided Cahill with all the run support he needed in the first inning when Aaron Hill, Upton and Mike Jacobs each delivered RBI hits to put the D-backs ahead early, 3-0.
An inning later, Hill added another run on a two-out RBI single to center before the club tacked on three in the fifth on a bases-loaded walk and Upton's two-run bomb off Cubs starter Justin Germano.
"I felt the curveball to Upton was the worst pitch I threw all night," Germano said. "It was definitely a hanger. I watched it on video, and I don't know how he hit it out, it was that bad of a pitch. They're an aggressive team."
Cahill capped off the D-backs' offensive assault in the seventh with an RBI single to right. He drove in two runs on the night.
"He was probably more excited about that than anything," Gibson said.