By Steve Keating

OMAHA, Nebraska (Reuters) - Katie Ledecky delivered everything but the world record everyone had expected, storming to victory in the women's 400 meters freestyle at the U.S. Olympic swim trials on Monday and securing her ticket to the Rio Games.

The dominant figure in women's swimming, Ledecky is a threat to smash a record almost every time she dives into a pool and she clearly had her sight set on lowering her own mark in the 400 free.

But the 19-year-old faded badly over the final 200, settling for the third fastest time ever in the event of three minutes, 58.98 seconds.

"I think the last 150 I just kept telling myself, Rio, Rio, Rio, just come on," said Ledecky. "I just tried to keep myself fired up on that and didn't really care what the time was.

"I haven't been 3:58 since 2014 and I'm happy how I swam it.

"I know there are improvements we can make off of it."

Ledecky, who came into the final having registered eight of the top 10 swims in the event, had looked poised to demolish her own mark of 3:58.37 when she blazed through the opening 200 meters more than two seconds under world record pace.

But the world champion had gone out too fast.

Losing time at each split in the final 200, Ledecky paid the price for her searing early pace. She was out of gas and even a delirious soldout crowd of 14,000 at the CenturyLink Center could not lift her to a new record.

Near the end, Ledecky was pushed by Leah Smith, who became the fourth fastest swimmer ever in the event when she touched in 4:00.65.

Entered in every freestyle event from the 50 to the 800 in Omaha, Ledecky will have many more chances at world records.

"I have the rest of the week ahead of me with a lot of big swims," she said. "I know I need to be fast the rest of the week so I am excited about heading to Rio and hopefully I can tack on a few more events."

But as always her focus will be on the races in which she has few rivals, the 200, 400 and 800 meters.

She owns the top times in the world in each event this year, and is seeking to qualify in all three and then chase a rare triple gold sweep at the Rio Olympics.

In other finals, Kelsi Worrell won the 100 meters butterfly, charging past 2012 Olympic champion and former world record holder Dana Vollmer to qualify for Rio.

Worrell, however, needed the second fastest time of the year to qualify for her first Olympic team, clocking 56.48 while Vollmer, returning to competition after having a baby, touched in 57.21.

Kevin Cordes is also headed to Rio after winning the men's 100 meters breaststroke in 59.18, beating Cody Miller to the wall by .08 seconds.

Hampered by a pulled groin, a battling Ryan Lochte fought through the pain to qualify for the men's 200 freestyle final with the fifth fastest time of 1:47.58.

Conor Dwyer, runner-up in the 400 free, will head into Tuesday's final as the top seed with a time of 1:46.96 but all eyes will be on 31-year-old Lochte, whose bid to secure a spot on a fourth Olympic team is threatened by an injured groin.

The 11-time Olympic medalist suffered the injury in the heats for the 400 individual medley on Sunday but has vowed to fight on.

(Editing by Andrew Both)