Zambrano (6-4, 4.34 ERA) threw 63 pitches, 38 for strikes. He is expected to be activated on July 16 when eligible to come off the DL. He will throw July 14 when the Cubs return from the All-Star break.
The right-hander gave up leadoff singles in the first two innings, but escaped without allowing a run. In the third, Beloit's Tobias Streich walked and moved up on a sacrifice bunt. Wang-Wei Lin was safe on an error by second baseman Arismendy Alcantara, which allowed Streich to score.
In the fourth, Zambrano walked the leadoff hitter but got the next batter to hit into a double play, then struck out Andy Leer.
Zambrano is headed to Guatemala on Sunday to complete paperwork in his adoption process of a 2-year-old boy whom the Cubs pitcher met when he was 5 months old. Zambrano's Big Z Foundation is donating clothing and 100 pairs of shoes to an orphanage as well.