Baseball Mogul (http://www.baseballmogul.com) says, "Then in 2001 we were the first to create a multi-player baseball management simulation." CSFBL officially launched on April 1, 2000.

Using the Wayback Machine, I found that the online beta of Baseball Mogul Online started on June 27, 2001. http://web.archive.org/web/20010721220129/http://baseballmogul.com/

Also using the Wayback Machine, we have proof that CSFBL was at least running on August 22, 2000: http://web.archive.org/web/20000822042859/http://www.csfbl.com/

Take it one step further, on February 1, 2000 we can see that we were already listed on MPOGD (http://www.mpogd.com) and were heavy into development of what was to be "version 3" of CSFBL.

Looks like CSFBL wins, and we can prove it!