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LOS ANGELES -- Eager to make a nice impression with his new team, Chris Johnson grounded into a double play with the bases loaded early in Monday night's game.

The next time up, he did a lot better.

Johnson hit a grand slam in his Arizona Diamondbacks debut, helping them beat the Los Angeles Dodgers 7-2.

"I just want to try to contribute somehow. I know I'm not going to hit a grand slam every night, so if I can just do the little things -- play some defense, run the bases, get some hits -- that's what I'm here for," he said.

Johnson, acquired Sunday in a trade with the Houston Astros, started at third base. He gave the D-backs a 7-0 lead in the fifth inning with his second career slam. Johnson became the first player in the Diamondbacks' 15-year history to hit a grand slam in his first game with the club.

Johnson connected off Aaron Harang after a two-out intentional walk to lefty-swinging Miguel Montero. At that point, Montero was 8-for-15 lifetime against Harang.

"I had a chance earlier in the game to do something and drive some runs in, and I kind of let the guys down. So I wanted to make up for that," Johnson said. "It's not that I was trying to hit a home run, but anytime a guy gets walked in front of you on purpose, you want to go up there and get a big hit.

Johnson left an Astros squad that had just broken a franchise record with their 12th straight loss and joined an Arizona team in playoff contention.

"One of the guys on the bench said, 'Anybody know what the Giants did tonight?' And that kind of shocked me, because I'm not really used to that," Johnson said.

"But it was intense out there, especially playing these guys. This team doesn't want to lose to those guys over there, so it was fun tonight. It seemed like opening day for me. My nerves were running wild tonight, but I settled down a little bit after about the fourth inning," he said.

Paul Goldschmidt hit a three-run shot in the first for Arizona.

Trevor Cahill (9-9) allowed a run and six hits over six innings with four strikeouts and three walks. The right-hander, acquired from Oakland in a multiplayer trade in December, is 3-0 with a 1.85 ERA in four career starts against the Dodgers.

Harang (7-6) gave up a season-high seven runs over five innings, along with nine hits and three walks. The 35-year-old right-hander is 1-7 with a 3.26 ERA in his past 12 starts against the Diamondbacks since beating them in consecutive starts with Cincinnati back in August 2003. During that stretch, they have homered off him 10 times.

The Dodgers, who concluded their 7-3 road trip with a three-game sweep at San Francisco that pulled them into a tie for the NL West lead, were coming off their first back-to-back shutouts of the season. But Harang found himself trailing 3-0 after just eight pitches, as Goldschmidt deposited his 1-0 offering behind the center-field fence for his 14th homer after singles by Gerardo Parra and Aaron Hill.

"The fact that two pitches were what changed the game was frustrating," Harang said. "It's tough to get two outs and give up a slam."

Cahill, who allowed first-inning runs in each of his previous seven outings, gave up a leadoff walk to Mark Ellis and a single by Juan Rivera -- who came in 1-for-15 against the right-hander. But Matt Kemp struck out and Andre Ethier grounded into a double play. Ethier, who had 55 RBIs in his first 63 games to lead the NL, has only six in 29 games and 102 at-bats since then -- and none in his past nine contests.

Game notes

Arizona 1B Lyle Overbay was designated for assignment to free up a roster spot for Johnson. … 3B Hanley Ramirez was 0-for-4 with a stolen base in his first home game for the Dodgers since they acquired him and LHP Randy Choate last Wednesday in a trade that sent Nathan Eovaldi and minor league RHP Scott McGough to Miami. In his 18 previous games at Dodger Stadium, Ramirez batted .388 with three homers and 10 RBIs. … Cahill is 9-0 with a 2.37 ERA in 10 starts this season when getting three or more runs of support, and 0-9 with a 5.23 ERA in his other 11 starts.