PHOENIX -- It's fair to say after 12 D-backs scored on Friday and 14 Dodgers crossed home plate on Saturday, each club's lineup reasoned that another big number on Sunday would earn victory.

Starting pitchers Dan Haren (seven stellar innings) and Chad Billingsley (six) had another scenario in mind.

Billingsley was very good, Haren was a skosh better, but the game was decided shortly after their exits: Dependable D-backs reliever Aaron Heilman (2-3) allowed Matt Kemp's towering two-run, go-ahead blast in the eighth, affording Los Angeles a narrow 3-1 victory before 26,517 at Chase Field.

"We made one mistake," interim Arizona manager Kirk Gibson said after his club's first game of the season's halfway mark, which pushed them a season-high 17 games off the National League West pace. "Aaron was trying to go in on him. If you watched the location, the previous pitch was right there; it tied [Kemp] up, and he pulled it. So we'll work on our execution."

"It wasn't meant to be where it was," added Heilman, who after an impressive start to the season has allowed runs in five of his last eight appearances. "I tried to make a good pitch and left it over the plate."

After newly minted All-Star Chris Young doubled in the eighth, the D-backs brought the potential tying run to the plate in Adam LaRoche, but he became Hong-Chih Kuo's sixth strikeout victim and the 14th of 16 for the game. Jonathan Broxton, credited with the latter two K's, pitched a 1-2-3 ninth.

"Not much to say after this one," said Haren, who had shut out the Dodgers for 13 1/3 consecutive innings dating to June 1 before yielding Andre Ethier's tying RBI single in the sixth. "Me and Billingsley kind of just went back and forth, and we both pitched pretty well out of jams. ... It was a good battle. I had a feeling it would be low-scoring."

Carrying the burden of two straight losses, Arizona hosts the Chicago Cubs, their first sub-.500 opponent since opposing the 17-19 Atlanta Braves on May 16, for a three-game series beginning Monday, when Ian Kennedy counters Tom Gorzelanny.

On Sunday, less than 24 hours after the D-backs' defense committed a franchise-worst six errors, Haren received plenty of defensive aid -- Miguel Montero caught James Loney stealing in the fourth and Kelly Johnson turned an unassisted double play in the fifth. His teammates just couldn't supply the run support.

The lineup did break through in the fourth against Billingsley with back-to-back extra-base hits. LaRoche doubled and scored a batter later on Mark Reynolds' triple high off the center-field wall.

But with Reynolds on third base and no outs -- as a sign that their situational hitting still needs work -- the next three Arizona hitters all struck out. The third, Johnson, came within feet of clearing the right-field foul pole for a two-run home run, before whiffing on Billingsley's 3-2 offering.

The inability to add on early cost the club late and, in the process, Haren, who has spun three straight quality starts but has just one win over that span.

Even though he knew the staff ace was expired after tossing 121 pitches (82 strikes), Gibson elected to let Haren hit for himself in the seventh. But the .408-hitting starter and the two batters behind him struck out against Kuo (3-1).

"He's got a [1.03] ERA, so I think he's something special," said Montero, who went 2-for-4 but struck out against Kuo in the eighth. "All their pitchers are pretty good."