Regan Smith of Lakeville set a world junior record in the 100-meter backstroke Thursday, finishing in 59.11 seconds to win her first gold medal at the world junior swimming championships in Indianapolis.

“It was insane,’’ Smith said. “After a kind of disappointing final [in the 200 back at last month’s world championships], I really wanted to come back strong at this meet.’

Smith, 15, recorded two superb performances in her first finals of the meet. In the 100 back, she beat Canada’s Taylor Ruck — who broke the world junior record in the semifinals with a time of 59.28 — by .12 of a second and seized the record. She swam even faster in the backstroke leg of the mixed 4x100 relay, clocking a 58.95 to lead off the event for the United States. The Americans won silver, .44 seconds behind Canada.

Smith finishing eighth in the 200 backstroke at the world championships in Hungary. She is swimming in the junior world meet for the first time. She also is entered in the 50 back, 200 back, 50 butterfly and 100 fly.