Led by quite a sister act, the Australians have set a world record in the 4x100-meter freestyle relay to beat an American squad anchored by Katie Ledecky at the Rio Olympics. Simone Manuel and Abbey Weitzeil put the United States ahead at the midway point Saturday night, but Bronte and Cate Campbell were simply too strong on the final two legs. Younger sister Bronte surged past Dana Vollmer before handing off to Cate, who pulled away from Ledecky to win in 3 minutes, 30.65 seconds — breaking the mark of 3:30.98 the Aussies set two years ago. The U.S. had to settle for silver in an American-record time of 3:31.89, extending a gold medal drought in the event that goes back to the 1996 Atlanta Games. Canada took the bronze in 3:32.89. The relay victory came on the heels of Mack Horton’s victory in the men’s 400 freestyle, capping an impressive first night for an Australian team that captured only one swimming gold medal in London four years ago.