Missy Franklin has given herself another chance to tie the record for the most gold medals at a world championships.
The 18-year-old American led the 200 backstroke heats Friday as she attempts to match Tracy Caulkins of the United States and Libby Trickett of Australia as the only women to win five events.
Caulkins won her five at the 1978 worlds in Berlin, while Trickett did it at her home championships in 2007 in Melbourne.
Franklin could match the record in the 100 freestyle final later Friday, although she's not the favorite in that event.
Michael Phelps holds the men's record with seven golds in 2007. And Phelps, of course, won eight at the 2008 Beijing Olympics.
The women's record for most gold medals at an Olympics is held by Kristin Otto of East Germany, who won six at the 1988 Seoul Games.
In the event in which she set a world record at last year's London Olympics, Franklin clocked 2 minutes, 7.57 seconds, 0.07 ahead of Belinda Hocking of Australia.
"I'm so excited it's the 200 back. I've been waiting for this the whole meet," Franklin said, before looking ahead to her evening schedule, which includes a 22-minute turnaround between the 100 free final and the 200 back semifinals.
"It will be my toughest turnaround," she said. "The good news is the 200 back is one of my favorite events. So I'll just swim the 100, see what happens, and then get a little shakeout and come right back for the 200. It's nice that I have the final before the semi, for sure."
Meanwhile, American teammate Katie Ledecky led the 800 freestyle in 8:20.65 as she goes for her fourth gold in her final event of the meet.
Also on Day 6 of eight in the pool, Evgeny Korotyshkin and Chad le Clos were the top qualifiers in the 100 butterfly -- the event that Phelps dominated at the past three Olympics and the last three worlds.
Korotyshkin led the heats in 51.55 and Le Clos, the man he shared the silver medal with in London, qualified second in 51.88. Ryan Lochte, who is racing this event for the first time at a major international meet, advanced 13th in 52.26.
In the foam-filled 50-meter free, Olympic champion Florent Manaudou of France was first in 21.72, with defending champion Cesar Cielo next in 21.76 and Andril Govorov of Ukraine third in 21.80.
Americans Anthony Ervin and Nathan Adrian qualified fifth and sixth, respectively, while freshly crowned 100 free champion James Magnussen got through in 11th.
"I didn't get much sleep last night. I just had to get through this morning and then hopefully get some rest," Magnussen said. "I feel like if I can get to that final anything can happen. My biggest hurdle is probably getting there."
The American men led the 4x200 free relay and Francesca Halsall of Britain and Jeanette Ottesen Gray of Denmark shared first in the 50 fly -- a non-Olympic event -- at 25.69.
Five finals were scheduled for later -- in the women's 100 free and 200 breast; and the men's 200 back, 200 breast and 4x200 free relay.