Summer McIntosh, top, competes against Katie Ledecky in the 400-meter...

Summer McIntosh, top, competes against Katie Ledecky in the 400-meter freestyle at the U.S. Open championships at the Greensboro Aquatic Center in Greensboro, N.C., Thursday, Nov. 30, 2023. Ledecky’s 13-year unbeaten streak in the 800-meter freestyle has ended. Canadian teenager Summer McIntosh finished almost six seconds ahead of Ledecky at a meet in Orlando, Florida, on Thursday, Feb. 9, 2024. Credit: AP/Woody Marshall

ORLANDO, Fla. — Katie Ledecky's 13-year unbeaten streak in the 800-meter freestyle is over, setting up a potential challenge from Canadian phenom Summer McIntosh at the Paris Olympics.

The 17-year-old McIntosh finished almost 6 seconds ahead of Ledecky at a sectional meet in Orlando on Thursday, becoming the second-fastest female in the history of a grueling event that Ledecky has dominated.

The teenager finished in 8 minutes, 11.39 seconds — an improvement on her previous best time by about 9 seconds. McIntosh went faster than Ledecky's winning time of 8:12.57 at the Tokyo Olympics.

It was the 26-year-old Ledecky's first defeat in an 800 free final since 2010. She finished behind American teammate Leah Smith in the preliminaries at the 2019 world championships, but bounced back to win the race that counted.

Ledecky has won three straight Olympic gold medals in the 800 free, and she's a six-time reigning world champion at that distance. She still holds the 16 fastest times ever, including her world record of 8:04.79 at the 2016 Rio de Janeiro Games.

Ledecky finished in 8:17:12 at the Orlando meet.

McIntosh and Ledecky both train in Florida, and the low-key sectional meet gave them a chance to do some racing after they joined many big-name swimmers in skipping the World Aquatics Championships in Doha, Qatar.

United States' Katie Ledecky holds up her gold medal after winning the women's 800-meter freestyle swimming final at the Aquatics Centre in the Olympic Park during the 2012 Summer Olympics in London, Friday, Aug. 3, 2012. Credit: AP/Lee Jin-man

This isn't the first time McIntosh has ended a long winning streak for Ledecky.

Late last year, McIntosh became the first swimmer in 11 years to beat Ledecky in a 400 free final held in the United States.

In March 2023, the teenager also snapped Ledecky's nine-year winning run in the 200 free in her home country.

The significance of McIntosh's latest victory is difficult to gauge, since swimmers are at different stages of their training cycles as they ramp up preparations for the Olympics.

Katie Ledecky competes in the women's 800-meter freestroke final at the World Swimming Championships in Fukuoka, Japan, Saturday, July 29, 2023. Given the unusual timing — a lingering fallout from the COVID-19 pandemic — many of the biggest names have decided to skip the World Aquatics Championships meet in Doha, Qatar. Credit: AP/David J. Phillip

Last summer, Ledecky turned in a dazzling time of 8:07.07 at the U.S. national championships in Indianapolis — her fastest time since setting the world record. So it's clear she wasn't in peak form for the Orlando meet.