Cubs infielder Mike Olt connected for a two-run shot in a three-run eighth that broke a 3-all tie.
Left-hander Tommy Milone, competing for a spot in the A's rotation, gave up three runs and five hits, including Ruggiano's homer, in three innings.
Cubs right-hander Kyle Hendricks gave up one run and one hit, a run-scoring single by Brandon Moss, in two innings. He walked three and struck out two.
''My mechanics were off, even in the bullpen,'' Hendricks said. ''I couldn't get a fastball where I wanted to save my life.''
Anthony Rizzo doubled and scored on Ruggiano's double in the first, then singled and scored on Ruggiano's homer in the third.
Josh Reddick went 2 for 3 for the A's, raising his average to .462. Moss finished 2 for 4 to stay at .500.
MIDDLE INFIELD OF FUTURE?
Top Cubs prospect Javier Baez could be paired with Starlin Castro in the infield soon. Baez is 4 for 9 with a double and a homer. But manager Rick Renteria said he still needs work, and the 21-year-old Baez is expected to spend the season in the minors.
''He has the bat speed to catch up to any fastball that anybody throws,'' Renteria said. ''Once he starts seeing more breaking balls and off-speed pitches, and they start trying to manipulate the zone with him, do I think he'll be able to ultimately, make that adjustment? Yes. Do I know he could hit `em now? No, I couldn't tell you that.''
Drafted ninth overall in the 2011 draft, Baez is a shortstop, the same position as Castro. And defensively, Castro and Baez have similar work ahead of them, Renteria said.
As they throw the ball ''there are a lot of times where they don't finish coming through a ball,'' he said. ''They'll catch a ball and stay flat-footed and kind of throw flat-footed,'' which sometimes results in throwing errors.
''They both have strong arms,'' Renteria added. ''So they depend on that and they like being able to show it.''
Both need to get to the point where the ''routine play is continually made,'' he said.
Milone indicated he took a nice step from his first start, in which he gave up three runs, including two homers, plus two walks in two innings.
''I felt like I improved a lot from the last game to this game,'' he said. ''Obviously, you look at the stats and it doesn't really look that way. But sometimes you gotta look past that.''
He added: ''The last time I walked two guys. The control wasn't really there. ... Today I felt a lot better. I threw a lot more strikes and had a lot more balls down in the zone.''
Milone says he does feel the stress of competition for a rotation spot.
''I guess I would probably be lying if I told you no; obviously in the back of my head, there's a little bit of that,'' Milone said. But in between the lines, I don't think about that at all.''
FULD'S SOLID SPRING
A's outfielder Sam Fuld went 1 for 3, with a double and a run scored. He is hitting .357 this spring.
The 32-year-old Fuld is a non-roster invitee who has six seasons of big league experience with the Cubs and Tampa Bay Rays.
''If there's room to improve, it's always on the offensive side for me,'' Fuld said. ''I'm always trying to do better with the bat. Sometimes you work as you want and you're not necessarily going to get results.''
He may make the big league roster only in the event of an injury, ''But I can't have that attitude. I'm under the impression that as long as I play well, good things will happen.''
Ted Lilly, who recently retired after pitching 15 seasons in the major leagues, including three-plus with the Cubs, has joined Chicago's front office as a special assistant to Theo Epstein, the team's president of baseball operations. Lilly helped the Cubs win NL Central 2007-08.
He will spend time during spring training, visit minor league teams during the season and evaluate amateur players leading up to the June draft as well as perform professional scouting.