Lakeville’s Regan Smith broke the world record in the women's 200-meter backstroke Friday at the world swimming championships.

The 17-year-old won her semifinal heat in 2 minutes, 3.35 seconds. That erased the old mark of 2:04.06 set by Missy Franklin at the 2012 London Olympics.

Smith lowered her own junior world record in the morning preliminaries, finishing in 2:06.01.

In the semifinals, she finished 3.22 seconds ahead of Kylie Masse of Canada, who was the second-fastest qualifier.

The final is Saturday night.