CHICAGO -- Jake Arrieta said he enjoyed running into some of his old Orioles teammates before Friday's game at Wrigley Field.
Then he had an even better time on the mound, shutting down Baltimore in his first start against his former club.
"There was a little more to it, being your former team," Arrieta said. "You know after the first inning, it was just kind of business as usual.
"It was nice to face those guys and see a lot of them again. It's been awhile."
The Orioles traded Arrieta to Chicago with reliever Pedro Strop in a multi-player deal during last season. He's turned into Chicago's ace this season.
"A really well-played game all the way around," Chicago manager Rick Renteria said. "The stage was actually set by Jake. Jake did a great job; a phenomenal seven innings of work.
Baez hit his sixth homer in his 18th game since getting called up from Triple-A, Luis Valbuena also homered, and Logan Watkins and Arismendy Alcantara each drove in runs with singles as the Cubs snapped AL East leading Baltimore's four-game winning streak.
Baltimore's Nelson Cruz hit his major league-leading 34th homer, a solo shot off Arrieta (7-4) in the seventh. It came on a change-up that Arrieta said "wasn't too bad of a pitch."
Cruz wasn't one of Arrieta's teammates on the Orioles, but he had faced the right-hander before.
"I think he looked more mature," Cruz said. "He has command of all his pitches. He doesn't make many mistakes."
Baltimore's Kevin Gausman (7-5) allowed three runs on six hits through five innings, He struck out seven.
Hector Rondon pitched a perfect ninth for his 20th save.
Arrieta retired the first 13 Baltimore hitters before Chris Davis lined a solid single to center with one out in the fifth, one of only two innings when the Orioles managed baserunners against Chicago's 6-foot-4 right-hander. He struck out five and walked only one.
Valbuena, batting cleanup with Starlin Castro out due to a family emergency, tied a career-high with his 12th homer that put the Cubs ahead 1-0 in the fourth. Ryan Sweeney doubled one out later, then scored on Watkins' single.
Baez hit a towering shot just inside the left-field foul pole, on a 3-2 pitch with two out in the fifth to make it 3-0.
Cruz ended Arrieta's shutout bid with a homer that reached the left field basket.
Orioles: A person familiar with the situation told The Associated Press that third baseman Manny Machado will "probably" have season-ending surgery on his injured right knee.
The person spoke to the AP on Friday under condition of anonymity because there was no official confirmation of Machado's plans. A decision was expected this weekend.
Yahoo! Sports first reported earlier in the day that the 22-year-old All-Star was likely done for the year.
Cubs: RHP Brian Schlitter, on the DL since Aug. 10 (right shoulder inflammation) has resumed throwing and made a relief appearance with the Cubs rookie league affiliate in Mesa, Arizona, on Thursday night.
Including Friday's game Cubs hitters have struck out 104 times in their last nine games. Baez, a free-swinging rookie had fanned 18 times in 33 at-bats. In his 18 games with Chicago, he has fanned 31 times.
"It feels good," Baez said of his homer on Friday. "I know I keep fighting to hit the ball hard. I'm not afraid to strike out, so I'm just going to keep throwing the bat."