OMAHA—The buildup started well before the Olympic trials did. As the field for the women's 100-meter backstroke began to take shape, a USA Swimming meet preview said the event was "set up to be one of the most talented fields of any race ever swum on US soil,'' calling it "an all-time race in the making.''

Round 1 went to Lakeville's Regan Smith. The top seed—and the world record holder until Sunday—swam the fastest time in Monday morning's preliminaries at CHI Health Center, finishing in 58.35 seconds. Her time is fourth-fastest in the world this year and outpaced the second-swiftest qualifiers, Rhyan White and Katharine Berkoff, by .53 of a second.

The top 16 women advanced to tonight's semifinals. Isabelle Stadden of Blaine, who swam next to Smith in the last of eight heats, also moved on. Her time of 59.53 was the sixth-fastest of the morning.

The 100 back field includes five of the six fastest American women ever to compete in the event. The seventh-fastest, Claire Curzan, scratched out of the race to focus on other events.

Other top contenders who advanced to the semifinals include 2016 Olympian Olivia Smoliga (59.24), Phoebe Bacon (59.32) and former world record holder Kathleen Baker (1:00.46). The top eight swimmers in the semifinals will move on to Tuesday night's finals.

Olympic trials on TV today: 5:30 p.m. NBCSN, 7 p.m. NBC

Smith's father, Paul, said Regan was "supremely confident'' as she walked to the pool Monday morning. She admitted to some nervousness in her first two swims Sunday, when she competed in the 100 butterfly on the opening day of the trials. Her world record in the 100 back also was toppled Sunday by Australia's Kaylee McKeown, whose time of 57.45 trimmed .12 from Smith's mark.

Though Smith reached the finals of the 100 fly, it is not one of her top events, so she decided to scratch from today's final to concentrate on the 100 back.

In her two 100 fly races, Smith didn't swim as well as she wanted to in the first 50 meters. She powered through the final 50 in both, displaying late speed that left her feeling optimistic.

Paul Smith said his daughter's nerves vanished this morning, leaving her relaxed and ready. Smith led the entire way in her preliminary heat and finished strongly again, with a time of 30.05 for the second half of the race.