Rusin, who was recalled from Double A Tennessee before the game, was pulled after the first four batters reached in the second. He was charged with five runs and eight hits in the Cubs' shortest start of the season.
Chicago used seven pitchers, five in the first five innings.
LaRoche had a solo shot and Moore belted a two-run drive off Rafael Dolis in the fourth. Zimmerman led off the sixth with his 18th homer off Miguel Socolovich and LaRoche connected for his 27th homer against Jeff Beliveau in the eighth.
Alfonso Soriano hit his 26th homer and a two-run triple for the Cubs, who have dropped four straight. Starlin Castro drove in two runs.
Chicago has eight losing streaks of at least four games this season.
In other games *
At Atlanta, Carlos Gonzalez hit his second home run since July 23 to give Colorado the lead, Jordan Pacheco also homered and drove in two runs, and the Rockies beat the Braves, 6-0.
Four pitchers combined on a nine-hit shutout. Carlos Torres (4-1), who took over after starter Drew Pomeranz lasted only three innings, threw three scoreless frames. He allowed three hits with no walks and three strikeouts.
Rex Brothers and Matt Belisle completed the shutout.
Gonzalez ended a scoreless tie with a one-out homer off Tommy Hanson in the fourth that landed deep into the centerfield seats.
Gonzalez, who had two hits, has 22 homers - including his most recent shot before Tuesday on Aug. 24.
Pacheco led off the fifth with his fourth homer for a 2-0 lead.
* At Miami, Norichika Aoki and Jeff Bianchi each homered and drove in three runs for the Milwaukee Brewers in an 8-4 win over the Marlins. Ryan Braun drove in Milwaukee's other two runs to give him 98 RBI, which leads the National League. The reigning NL MVP is looking for his fifth straight season with 100 RBI.
The Brewers' Kameron Loe (6-4) and Marlins' Mike Dunn (0-2) each faced one batter and threw just two pitches.
Giancarlo Stanton hit his 30th home run and Gorkys Hernandez hit his first career long ball for the Marlins.
It's Stanton's second consecutive 30-homer season despite missing 30 games following knee surgery in July. He hit 34 in 2011 after hitting 22 as a rookie.
* At St. Louis, Jon Jay and David Freese went 2-for-4 each and drove in a run each as the Cardinals defeated the Mets, 5-1. Jaime Garcia (4-6) scattered nine hits in 7 2/3 inning to pick up the win for St. Louis.
The Mets' only run came on Mike Baxter's sacrifice fly in the eighth, which knocked in Justin Turner.
St. Louis Cardinals pitcher Chris Carpenter, recovering from surgery to relieve nerve compression that left much of the right side of his body numb, threw a simulated game.
The 37-year-old righthander underwent surgery in July, with the hope he could return for spring training. He upped the ante Tuesday, 4 days after working two innings in Washington.
"It was a good day," Carpenter said. "Hopefully the next few days I'll recover nicely and we'll do it again."
Cardinals manager Mike Matheny was enthusiastic, too.
"The ball was jumping out of his hand. It's really in his finish," Matheny said. "He has sink, he has cut, which he wasn't really able to do before."
Still, Matheny is trying his best to keep expectations realistic for a pitcher sidelined since spring training. Several times he sidestepped questions, and grew increasingly annoyed, when asked when the 2005 NL Cy Young winner might be ready or how he would be used - or even if he would be used in the postseason without throwing in the regular season.
* The Washington Nationals reinstated righthander Chien-Ming Wang (hip) from the 15-day disabled list.