The U.S. (1-1) meets Canada (1-1) in the final game of Pool D play on Sunday with the winner advancing to the second round.
Ryan Vogelsong settled down after a shaky start to get the victory. The San Francisco right-hander went four-plus innings, allowing two runs and six hits, striking out four.
The U.S., bouncing back from Friday night's 5-2 loss to Mexico, fell behind 2-0 after two innings but shut the Italian squad down on two hits the rest of the way.
Italy (2-1) clinched a second-round berth for the first time in its WBC history when Mexico lost to Canada earlier Saturday.