Aaron Peirsol has reclaimed his world record in the 100-meter backstroke at the U.S. national championships.

The Olympic champion trailed Matt Grevers at 50 meters, then poured it on down the stretch to win in 51.94 seconds, becoming the first person ever to swim under 52 seconds in the event.

Peirsol's previous mark of 52.54 set at the Beijing Olympics was broken by Spain's Aschwin Wildeboer Faber on July 1. Faber swam 52.38 on the backstroke leg of the 400 medley relay at the Mediterranean Games.

Grevers, the Olympic silver medalist, finished second in 53.11.

It was the sixth time Peirsol has lowered the world record in the 100 back, an event he has dominated for most of the decade.