Serena Williams and Steffi Graf played twice in 1999. Each won one. Both matches went to three sets.
Starting next week at the US Open, Williams will be trying to match Graf's calendar Grand Slam from 1988 and also pull even in the majors department with 22.
Here's a comparison of some of their key head-to-head numbers.
Career WTA titles
Majors played
Major titles
Runner-up finishes at majors
Career record at majors
Where their majors were won
Career record
Total weeks at No. 1
Career prize money
(not adjusted for inflation)