ATLANTA (AP) — Olympian Tom Shields has set an American record in the 100-yard butterfly at the U.S. Winter Nationals.

Shields, who won a gold medal in Rio as part of the 4x100-meter medley relay, became the first swimmer to break 44 seconds in the event. He won Friday night with a time of 43.84, eclipsing the record of 44.18 that was set by Austin Staab in 2009.

Shields also beat the U.S. Open record of 44.01, set by Singapore's Joseph Schooling at the 2016 NCAA championships. Schooling went on to beat Michael Phelps for the gold medal in the 100 fly at the Rio Olympics, with Shields finishing seventh.

The Winter Nationals are being held at Georgia Tech in the lead-up to the short-course world championships, which begin Tuesday in Windsor, Canada.