Near the end of his second set on Saturday, Milos Raonic reared back and cannoned a 143 mph serve across the net.
Several terrible things happened in the next fraction of a second.
The line-judge jumped to get of the way. A ball boy standing alongside her was momentarily unsighted. At the last instant, he realized what was coming at him. He tried to throw himself to safety, but was hemmed in by a scoreboard. The ball popped up and nailed him in the nethers.
How to describe the noise the crowd made at that moment? It was an animal groan. That was real empathy in action – at least from half of them.
The kid leaned over for a moment, then gave the crowd that tight 'No, no, I'm alright. I'm alright' smile we all slap on right after we've walked into a phone pole or gone head first down a flight of stairs.
"I didn't know I'd hit him in a very sensitive spot because the guy stood up pretty well. I'm not sure I would if something hit me there at 143 miles an hour," Raonic said afterward.
Did you say anything to him later?
"It was the middle of a tiebreak. It's really hard to come out of that (mindset). I didn't have an image in my mind of which ball boy it was."
One supposes that that unfortunate young man will have a fairly fixed image of Raonic burned onto his lizard brain for the rest of his life.
Once again, it was a combination of a huge serve, and his faith in it, that propelled Raonic past inferior opposition.
Afterward, late-in-life Cinderella Victor Estrella Burgos would say that this was his best match of the tournament. He was able to string Raonic along to three consecutive tiebreaks, and then narrowly lose each one. The match finished 7-6(5), 7-6(5), 7-6(3).
We haven't seen anything close to the best from Raonic here in New York. Having done just enough to get by three opponents, he's been philosophic about it.
"I believe I can play better," Raonic said. "I believe I will."
Suddenly, he'll have to.
His next opponent is 10th ranked Kei Nishikori.
The Japanese is, in many ways, Raonic's mirror image – a player who relies on speed and movement to keep him in points. The pair met in the fourth round at Wimbledon. Raonic took him in four sets.
On the slower hardcourt surface, the advantage tilts slightly toward Nishikori. He's taken two of three from Raonic over the past three years.
Raonic's team has talked about their player girding his strength here – not expending too much energy on inferior opposition. Now that he's reached the final 16, it's time to take it up several gears. If he can get past Nishikori, his likely quarterfinal opponent is Australian Open champion Stan Wawrinka.
That makes Saturday the fork in Raonic's U.S. Open road. He can't coast any more.
This did provide one last opportunity to ask goofy questions, and expect fun answers.
Someone finally brought up the hair. Raonic's hair is clearly brilled into sculpture, and has become a point of fascination with some ESPN talking heads. Apparently, Patrick McEnroe can't stop talking about it.
What do you put in it?
"The right product," Raonic said.
"Maybe you'll get an endorsement deal," the questioner prodded.
"Maybe I will. But I'm not necessarily chasing one at the moment. I'll just let the hair speak for itself. It's got a Twitter account (@milosraonichair)."
He doesn't want to say the product, because he doesn't want to scare off a dozen other hair products that might be willing to sign him up.
If he can deploy a little more of that sort of quick thinking on the court, we're in for a very fun ride over the next few days.