Katie Ledecky of Bethesda after competing in the Women's 800-meter freestyle heats Friday at the FINA Swimming World Championships in Kazan, Russia. (Valdrin Xhemaj/EPA)

For her penultimate swim of the FINA World Championships, Katie Ledecky, the 18-year-old Bethesda native and the sport’s resident phenomenon, delivered a performance that, in its own way, was as remarkable as any she has produced during this meet. In the preliminary heats of the women’s 800-meter freestyle Friday morning, she looked decidedly human. But don’t be fooled.

For any actual mortal — which is to say, any competitor besides herself — Ledecky’s time of 8 minutes 19.42 seconds would have represented an unfathomably fast race. Only one other swimmer in the world had gone faster than that in the past 24 months.

But for Ledecky, who has spent the past five days at Kazan Arena rewriting the record book and leaving little doubt she is the top performer in the world right now, that time represented an off-day, a swim that did what she set out to do — win the qualifying heats and give her the top spot in Saturday night’s final — but little else.

“I wasn’t really focusing on a time or anything,” said Ledecky, the world record holder in the event at 8:11.00. “I dove in, started out and knew it wasn’t going to be anything special, so I just kind of went through it. I just needed to get a good spot for the finals tomorrow.”

Olympic gold medalist Katie Ledecky broke multiple world swimming records before graduating high school. Now in her senior year in Bethesda, Md., she’s wrapping up her high school swimming career and looking forward to World Championships this summer. (Zoeann Murphy/The Washington Post)

Those final is almost certain to see the other version of Ledecky, the one that has left the rest of the world awestruck. Over the previous five days, she has swum 4,600 competitive meters, earned four gold medals, set a pair of world records (both in the 1,500 free) and pulled off a stunning 1,500-200 “double” with less than 30 minutes in between — the first half of which produced a world record and the second half a blistering final lap that narrowly advanced her out of the semifinals of the 200.

She insisted after Friday’s 800 prelims that she wasn’t tired or feeling the aftereffect of Tuesday’s double. “That’s long gone,” she said. “That feels like years ago.” More likely, she was merely coasting through a prelim race, which she had the luxury to do. When she wants to kick it in again, as she almost certainly will Saturday night, she knows it will be there.

Still, after seeing her set a world record in the 1,500 prelims four days ago — a mark that surprised even her — it was almost unsettling to see Ledecky struggle to shake her closest pursuers down the stretch of a major international distance race. No one in the world-class field had been within 10 seconds of her all year in the 800, but as the swimmers hit the final lap, both Denmark’s Lotte Friis and New Zealand’s Lauren Boyle were within 1 1/2 lengths of her.

“I could feel them coming,” Ledecky acknowledged.

Ledecky’s time Friday was well off her best. She hadn’t gone that slow in the 800 in a meaningful final since the 2012 U.S. Olympic trials, when she was 15 years old. Of course, after that showing, her next try at that distance produced the crowning moment of her career to this point — her gold medal at the 2012 London Olympics.

As another Olympic quadrennial cycle enters the home stretch, with the 2016 Rio de Janeiro Olympics now less than a year away, Ledecky faces one last swim here, Saturday night’s 800 free final, before heading home and turning her sights toward Rio.

And it is a safe bet she will not be holding anything back Saturday night. At stake is not only a fifth gold medal but an unprecedented sweep of the 200, 400, 800 and 1,500 freestyles.

“I always like to finish on a good note and finish the season well and come away with a good feeling,” she said, “so hopefully I can put together something good.”