PERTH, Australia — Serena Williams and Roger Federer have athletic lives of almost parallel excellence, which will finally intersect on a tennis court Tuesday.

The 37-year-olds are the only people to have won 20 or more Grand Slam singles titles in the Open Era besides Steffi Graf, who has won 22. Williams’ 23 and Federer’s 20 are the most of Grand Slam singles titles of any woman and man, respectively, in the Open Era. They have won Grand Slam titles on the same court on the same weekend eight times, first in 2003 and most recently in 2017. Each has made comfortably more than $100 million in prize money and endorsements.

They have been headliners on posters and played consecutively on a center court many times, the two have never faced each other on a court in their decades together on tour (they did play on the same team in an exhibition match in 2010 to raise money for Haiti). That will change New Year’s Day at the Hopman Cup, where Federer and Williams will be across the net from one another in a mixed doubles match between Switzerland and the United States.

“I’ve been looking forward to it since I saw it,” Williams said. “I was like, ‘Oh, my God, this is so cool.’ So it’s just something that, as a player, is something that you would dream of, to play Roger Federer.”