The hype around Serena Williams' potential swansong tournament is "the biggest thing I've ever seen in women's tennis", says Torben Beltz, the coach of her next opponent Anett Kontaveit.
Williams has announced she is soon to retire, and the US Open is widely expected to be her final tournament.
The 23-time grand slam champion came through in straight sets in her first-round match against Danka Kovinic to set up a tough meeting with world number two Kontaveit on Wednesday.
Beltz wanted to watch Williams' opening match but could not do so after Arthur Ashe Stadium sold out, with reports of tickets on the secondary market on sale for around $1,000.
And Beltz says he has not seen anything like it, telling the New York Times: "I couldn't get a ticket.
"This is the biggest thing I've ever seen in women's tennis. I think it's the greatest thing for the sport, and we all have to thank Serena for all she did. Especially right now with the end coming."
While Beltz's charge Kontaveit is favourite for the second-round match, the Estonian's coach knows it will be a tough match against the six-time US Open champion.
"I think her ball speed, serve and return is really up to her prime time," Beltz added.
"I saw her other matches, and it looks like she's improved over the last couple of weeks. She looks in better shape and looks good now.
"For Anett, I think the key is to just go out and try to play her best tennis but also enjoy the moment. It's going to be a big challenge, a great challenge, but I think she wants that challenge and wants to embrace it."