A 21-game winner last season, the right-hander is just one victory over .500 with a 12-11 record and an unremarkable 4.39 ERA.
Perhaps the biggest reason for Kennedy's decline has been his vulnerability to the long ball.
Allowing just 19 home runs last year, the 27-year-old has surrendered 27 already this season, including 13 in his last nine starts.
Kennedy will attempt to keep the ball in the park Tuesday, when the D-backs welcome the Dodgers to Chase Field to open up a two-game series between the National League West division rivals.
"Solo home runs, they're going to happen," Kennedy said. "I wish they didn't, but the two-run homers, especially after they scored one, those are the ones you try to avoid. It's not like I'm going out there trying to not give up homers because it's just going to happen."
In his last outing, Kennedy allowed five earned runs on seven hits over 5 2/3 innings against the Giants. Despite his sub-par performance, the D-backs ended up capturing the victory over San Francisco.
While the D-backs know Kennedy will be on the mound for them on Tuesday, the Dodgers still are unsure who will be pitching for them.
Los Angeles ace Clayton Kershaw was scratched from his start on Sunday because of a sore hip but could pitch Tuesday. If he is unable to go, right-hander Aaron Harang might get bumped up from Wednesday's scheduled start, but Dodgers officials said Sunday they were hopeful Kershaw would start Tuesday.
Kershaw underwent a contrast MRI, which revealed no structural damage, and tried to make Sunday's start.
"I felt good enough to pitch today. It wasn't my decision," Kershaw said. "I would have loved to pitch today, yeah. It put Donnie in a tough spot, I understand that. He had to do what he felt was best."
As for manager Don Mattingly, he said he's thinking about what's best for Kershaw and the Dodgers.
"I want him to be in the best position to pitch the rest of the year," Mattingly said. "We have 20-something games left. ... This is all about his best chance to be healthy the rest of the way."
Dodgers: In his own League
Reliever Brandon League has pitched scoreless relief in his last 11 appearances (11 2/3 innings) since Aug. 21, allowing four hits (4-for-38, .105) with 15 strikeouts, and picking up both a win (Sept. 3) and two saves (Sept. 1, Sept. 8) in that span. It's the longest scoreless stretch for a Dodgers reliever this season.
Hanley Ramirez has nine home runs in his last 23 games and 10 in 43 games with the Dodgers. Four of his last 12 hits have been home runs.
Lefty reliever Randy Choate has held left-handed hitters to a .157 mark (14-for-89) this season.
D-backs: Miley staying grounded
Starting pitcher Wade Miley is entering rarefied rookie air as the season winds down. With his win Saturday, the 25-year-old now has 15 on the season, the second most for a National League rookie since 1986.
Certainly a season like this would exceed any rookie's expectations. But for Miley, being among the top starting pitchers in his first full season simply wasn't on the radar.
"I kind of expected to be in the bullpen, so I really didn't expect much," Miley said. "Just wanted to get in the clubhouse and not look back. I've always been a starter, I like doing it, so when I got an opportunity I didn't want to lose it."
His 3.07 ERA is the best among all first-year hurlers who've started more than 18 games.
"It's whatever. I don't put too much thought on that stuff," Miley said. "If it happens, it happens. If not, I'm going to wake up the next morning and do whatever. It's not going to break my heart or anything."
Dodgers first baseman Adrian Gonzalez ranks second in the Majors with a .387 batting average (58-for-150) with runners in scoring position.
Paul Goldschmidt (39 doubles) and Aaron Hill (35 doubles) are on pace to become the fifth and sixth players to reach the 40-doubles plateau in D-backs history.