Katie Ledecky opened USA Swimming's world championships trials with a blistering 800-meter freestyle triumph, clocking eight minutes and 07.07 seconds on Tuesday in her fastest performance since setting the world record in 2016.

Ledecky, who won at the Rio de Janeiro Olympics Games in a world record-setting 8:04.79, posted the third-fastest time ever in an event she has dominated since winning it on her Olympic debut in 2012.

Ledecky became the sixth American swimmer to qualify for a sixth long course world championships team, joining an elite group that includes Michael Phelps, Natalie Coughlin, Ryan Lochte, Elizabeth Beisel and Nathan Adrian.

"It felt great," said Ledecky, who has won the 800m free at three straight Olympics and five straight world championships.

"I've been so eager just to get the meet started, just watching all the fast swimming today," added Ledecky, whose performance highlighted the opening day of the US trials in Indianapolis, Indiana.

"I was happy with that time."

Jillian Cox cut 10 seconds off her personal best to finish second in 8:20.28 and punch her ticket to the world championships next month in Fukuoka, Japan.

Jack Alexy won the men's 100m freestyle, leading from start to finish to edge a tightly-bunched field in 47.93 seconds.

'I was happy with that time.'

Collegiate standout Chris Guiliano was a surprise second in 47.98 — his second personal best on the day.

Caeleb Dressel, whose five gold medals at the Tokyo Olympics included the 100m free, finished 29th overall in the preliminaries — last in his heat.

Dressel, a seven-time Olympic gold medalist and 14-time World Champion, withdrew from last year's World Championships in Budapest citing unspecified medical reasons and hadn't returned to competition until a low-key meet in Atlanta last month.

The 26-year-old is entered in three more events this week, the 50m free and the 50m and 100m butterfly.

Kate Douglass won the women's 100m free, surging home for a victory in 52.57 seconds — the fourth-fastest in the world this year.

Douglass, recently turned pro after a final standout collegiate season, had broken 53 seconds for the first time in the heats.

Abbey Weitzeil, unable to match her 52.92 of the morning, clocked 53.11 to grab second place. Last year's world championships bronze medalist Torri Huske was fifth.

Regan Smith won the women's 200m butterfly in 2:05.79 ahead of training mate Lindsay Looney (2:07.35).

Smith grabbed Olympic silver in the event in Tokyo and since a fourth-placed finish at last year's world championships she has made a move to Arizona to train under Michael Phelps's former coach Bob Bowman with her sights set on the Paris Olympics.