NEW YORK -- Kateryna Bondarenko, who had just won her second-round singles match, was collecting her things at the changeover chair Wednesday night when a man named Sam Hu jumped off the three-foot ledge that separates Court 13 from the stands.
Hu landed awkwardly but turned deftly toward the seats and slipped his left arm around her back. Bondarenko, almost reflexively, responded in kind with her right arm, awaiting the imminent photo opportunity.
As a friend in the stands snapped the shot, Hu, hip to hip with Bondarenko, gleefully gave a thumbs up and said, "Beautiful, beautiful."
Two security guards, who arrived at the scene six seconds after he arrived, actually waited several more seconds as the photographer wrapped up. Bondarenko smiled as Hu, 47, was hustled away, amid applause and laughter.
If Hu had intended to harm her, certainly he was in a position to do so.
"Six seconds," said Bethanie Mattek-Sands, a heavily decorated American doubles player, "can be a long, long time. Anything could happen, even that fast."
And that's the difficult piece of this incident. The two assigned security guards reacted swiftly, but not fast enough, to prevent a potential assault.
Earlier this summer, an extraordinary video surfaced that showed a fan jumping down into the players' tunnel after a friendly between Lionel Messi's Barcelona and the home-team Celtic in Dublin. The fan lands on his feet and, just as he attempts to embrace Messi, a security guard decks him with a chest-high flying tackle. Mike Rodriguez, the USTA's director of security, said that tennis, like basketball, is a tough assignment.
"It's difficult to guard a court," Rodriguez said Thursday. "We are dealing with human beings, so training and focus are always a factor.
"We got the word out last night. There is a reaction if you try to take that action."
New York police made the arrest, charged Hu with interference of a sporting event, recently upgraded to a misdemeanor, and took him to the station house of the 110th precinct.
On Thursday, Hu was released and active on Chinese social media Thursday. He owns a tennis academy near Shanghai, China, but lives in Long Island.
"Learn from this lesson," he wrote on Weichat. "Man [need] to control himself, control, control."
As part of the US Open protocol, Hu has been banned from the event for 10 years.
Bondarenko, whose doubles match was canceled Thursday because of rain, was not available for comment.
The incident recalled last year's French Open, when a spectator seeking a selfie with Roger Federer ran onto the court and made contact before security intervened. Afterward, security was visibly heightened. It was another ultimately benign example of star worship, but the opportunity for foul play was there.
"I feel safe," insisted No. 5 seed Simona Halep after her second-round victory. "Nothing happened to me until now. No one wants to hurt you, even if someone is coming to take a picture with you."
But in 1993, when Bondarenko was a 6-year-old playing tennis in the Ukraine, Monica Seles was stabbed in the back while sitting on her changeover chair in Hamburg. Gunter Parche, a crazed supporter of Steffi Graf, drove a nine-inch boning knife between Seles' shoulder blades. Seles, who had won eight Grand Slam singles titles before her 20th birthday, did not play another match for more than two years. Upon her return, Seles was never the same.
That was 23 years ago. Today, terrorism and security occupy a far more significant place in our consciousness.
"This is more than just a tennis tournament we're talking about; it's the world," said Patrick McEnroe, the former USTA general manager of player development. "You do everything right, and there's still that opportunity. At some point, you have to just trust in the world."
McEnroe, citing the increased presence of x-ray machines at the gates and more aggressive bag checks, reminisced about the old days, when security was more of an afterthought.
No. 2 seed Andy Murray said safety concerns surface more when he's off the court.
"When I am out in the streets and stuff, I think more about that," he said. "Not just because of the things that have happened in the world, like in the big cities over the last 15, 20 years.
"When I'm at a tennis tournament, I don't know; I just feel comfortable when I'm on the court."
Murray related the anecdote of a kid who leaped onto the court after a match at the Olympics in Rio de Janeiro.
"I had signed his hat, and then gone away with his pen," Murray said. "He jumped onto the court and asked for the pen back."
According to Rodriguez, the USTA, NYPD and security force regularly engage in tactical exercises.
"Look, there are plenty of examples in the tennis world, never mind the sporting world," he said. "People come on the court to get a selfie, kiss someone, hug them. In our training, we remind people that what you're seeing might not be what you think it is. You need to [be] prepared when it's not that.
"You can't just think it's not a big deal. Everything is important."
Brad Gilbert, coach of Andre Agassi, Andy Roddick and Andy Murray, shook his head when Bondarenko's incident was described to him.
"If someone wanted to do something, that's pretty hard to defend," said Gilbert, an ESPN analyst. "If they're crazy enough to try it, the opportunity is there.
"The fact that he could get that close to her, man. My guess is the debriefing room is not a pleasant place today."
He's right. Video of the episode was posted on Instagram, and Rodriguez said it generated hundreds of thousands of views. He forwarded it to the private security company responsible.
"This is what we do on the counter-terrorism side," explained Rodriguez, who comes from that background. "I said, 'You need to use this as a training aid, a positive reinforcement. But we need to pay a little more attention to people understanding what they need to do."
All told, Rodriguez said, there are close to 300 security guards and an equal number of New York City police on site every day. Seven or eight people are deployed for the show courts, where the players and attention they generate are greater, and a minimum of two, plus one for relief, on the field courts. In addition, two people from player operations escort players to and from the courts.
"It stops and makes you think," Mattek-Sands said. "But it's the world we live in."