"I thought I was going to die," Caroline Wozniacki gasped, moments after completing the New York City Marathon today. She did anything but that, clocking an impressive time of three hours and 26 minutes. That's a 7:53-per-mile pace. The secret? Filling up on popcorn the night before, while hanging out with seemingly perpetual pal Serena Williams at a New York Rangers hockey game.

Advertising

After finishing, Wozniacki labeled the 26.2-mile race, which took place in temperatures in the low 40s (Fahrenheit), her "toughest physical test ever."

Advertising

Here, Serena's Instagram clip from the finish line:

Advertising

The tennis stars' friendship can't be overstated, as it turns out. Serena even placed a finisher's medal around Wozniacki's neck with ESPN2 cameras rolling.

Advertising

And briefly, the tables turned—via this footage of Serena proudly recording Wozniacki at the finish line.

Advertising

Wozniacki decided a week before Wimbledon in June to run the race, and did so on behalf of the charity Team for Kids, comprised of adult runners who seek to raise funds to give healthy opportunities to underprivileged children who otherwise have little access to regular physical activity. Wozniacki raised about $81,500 for the cause ahead of the race.

Wozniacki had received cautionary advice from the likes of Amelie Mauresmo, who ran the New York City Marathon herself in November 2010, nearly a year after retiring from professional tennis. Said Wozniacki, "She told me it's so hard, and she said, 'I don't understand how you can do this while you're playing?' She was encouraging me, but at the same time, she was shaking her head a little bit, thought I was a little crazy. I think I beat her time here, didn't I? I did beat her time. Wow, so yeah, I'm proud of that."

Indeed, Mauresmo's time was three hours, 40 minutes—14 minutes slower. A week removed from her competition in the WTA Finals in Singapore, where she reached the semifinals before losing a close contest to Serena, and on the heels of her Saturday-evening social schedule with that same friendly foe, it's time to start talking about Wozniacki's place among the absolute best athletes on the planet. Because this display, friends, is true fitness.

Got a tip or a point to make? Hit me on Twitter at @jonscott9.