Stanford sophomore Simone Manuel finished sixth overall in the semifinals of the 100-meter freestyle Thursday at the FINA World Championships in Kazan, Russia.
She advances into Friday night's final, along with Missy Franklin, who claimed the final spot by placing eighth.
Ledecky's leg was the quickest for Team USA, which captured its third straight 800 freestyle relay world title.
Franklin captured her record 10th World Championship gold, while Ledecky won her eighth in eight career events.
Ledecky finished a furious comeback to get teammates Missy Franklin, Leah Smith and Katie McLaughlin to the top of the podium. The eight-time World Championship gold medalist clocked a 1:55.64 final 200 as the American's won in 7:45.37.
Italy (7:48.41) and China (7:49.10) went 2-3. Sweden led for the first three legs before falling back to fourth.
Manuel, the reigning 100 freestyle NCAA champion, placed seventh in prelims and sixth in the semifinals, in 53.81, to take the No. 6 seed Friday night.