Tennis players are a superstitious bunch. And so, too, it turns out are many coaches.

Among their number is Torben Beltz, coach to World No.1 Angelique Kerber. “I think I’m more superstitious than her maybe,” Beltz told CNN’s Open Court after his charge lifted the US Open title earlier this month.

The current ritual, which began during her New York run, leaves Beltz in danger of departing Asia looking even more hirsute than usual: “When she’s winning, I’m not shaving.”

And for this week’s Dongfeng Motor Wuhan Open, Beltz has upped the stakes, agreeing with the new World No.1 that he would sport a mustache for the remainder of the season should she lift any further silverware during the Asian leg of the tour.

“In the past when I was playing I didn’t shave, and I still keep on doing this as a coach,” Beltz said. “If she keeps on winning for two weeks like here it’s getting really big my beard.”

In the latest edition of Open Court, Kerber and Beltz discussed rising up the ranking, the secret behind their close bond and, of course, shaving habits…