In his 100th career start, Arrieta scattered four hits over seven innings, and he improved to 4-0 in five career starts against Pittsburgh. He's given up nine earned runs over 30 innings in those games.
"This guy has turned into such a high-end professional," Cubs manager Joe Maddon said. "He just settled down, made better pitches, controlled his emotions, and he was wonderful."
The Pirates were on the attack in the first inning, and their aggressive approach actually helped the right-hander.
"We felt they didn't want to get deep in the counts and were trying to get a swing on the first fastball they saw near the zone," Arrieta said. "That's kind of what happened in the first.
"I knew, based on the pitch count, I still had the opportunity to pitch deep," Arrieta said. "To do that, I needed to focus on early strikes down in the zone."
Arrieta didn't allow a hit after the first until there were two outs in the sixth. He got plenty of offense, as rookie Kris Bryant drove in three runs and scored another.
"Our offense is going to win us a ton of games this year," Arrieta said. "We have a special lineup -- a lot of young players, but with the addition of Bryant now, it takes the pressure off [Jorge] Soler, [Anthony] Rizzo and [Starlin] Castro. We're moving in an incredibly solid direction and it's fun to be a part of it."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.