While these circumstances alone are awe-inspiring, what made the experience truly special was being in King’s presence as she watched the day’s match featuring, in her words, “the best player the game has ever seen.” Roger Federer defeated Luxembourger Gilles Muller in a quarterfinal that, although only three sets, included two tiebreakers.

While you might expect that someone who has been around tennis all her life would be somewhat immune to its thrills, the opposite seems to have happened with King, whose U.S. Open badge reads “former champion.” (Does this do her justice?) She’s more zealous than ever, particularly when it comes to her man Federer. Watching on the big screen in her suite, she leapt from her chair, clapping her hands during a hard-fought point, “Come on baby!” She paced around the room, seemingly imagining herself on the court with him, calling out “Oh, you got lucky!” Enraptured by Federer’s serve, she murmured, “Great kinetic linkage.”

A few shots later, she chided him, “That was the wrong volley anyway,” and again jumped up to demonstrate how the shot should have been executed. With King, you not only get pithy commentary but instruction too. At one point she walked up to the screen, pointing at the court to explain where the players were aiming their serves and why.

King’s co-spectators included several tennis fans who are also big players in the world of golf: Dawn Hudson, former CEO of Pepsi-Cola North America (and on last year’s Fortune Most Powerful Women list) and current chairwoman of the LPGA, and Karen Durkin, former CMO of the LPGA and new CEO of the Women’s Sports Foundation. We got talking about similarities between tennis and golf and King held that all tennis players should be good golfers and vice versa, “It’s all about point of contact!” she said told us. But she noted that golfers tend to screw up the backhand. “The forehand is familar to them, but they avoid the backhand.” Thanks to Billie Jean, I now know why I’m better on the course than the court.

By the way, Pattie ran into former Altria CEO Geoff Bible and had a lively chat with him. She’ll tell you about that on Monday. Have a great weekend. – Jessica Shambora

Read Billie Jean King’s guest post on Postcards, Champions adjust.