BEIJING — Shawn Johnson finally got her Olympic gold medal in the last event of the women’s competition Tuesday night, the balance beam.

Johnson nailed her routine that is chock-full of difficult tricks, earning a 16.225. Her grin was a thousand times wider than the 4-inch-wide beam she had just conquered.

The world champion, who already had a silver behind fellow American Nastia Liukin in the all-around, and a silver on floor and in the team event, edged Liukin, who finished with a gold, three silvers and a bronze.

Cheng Fei of China took the bronze, giving China six women’s medals, two behind the U.S.