U.S. advances in 4x400 women's relay, Poland flexes muscles again

TOKYO -- The United States easily advanced to the final of the women's 4x400m relay on Thursday, winning its heat in a scorching 3:20.86.

The 2016 gold medalist and reigning world champion had a slight lead going into the final leg and anchor Lynna Irby charged through the last lap to win the heat by more than a second, with Jamaica and Britain also advancing.

Poland won its heat in 3:23.10, in another impressive performance after its upset win in the inaugural mixed event last week, as Cuba finished second and Belgium third in a national record 3:24.08.

Six-time Olympic gold medalist Allyson Felix is expected to join the U.S. team for Saturday's final, in her fifth and final Games.