BERLIN—American swimmer Peter Marshall broke his own world record in the 100-meter backstroke Saturday on the first day of the short-course World Cup meet.

Marshall clocked 49.64 seconds, 0.30 faster than the record he set earlier in the week in Stockholm—where he also broke the 50 backstroke record.

American Randall Bal finished second in 50.55.

Marshall said he still had room to improve.

“The last stroke was a little too long, this is why I didn’t touch so well,” Marshall said. “I’m a bit surprised by my performances during the World Cup series...

Log-In to view full story or view our Registration Guide.