There is only one bus that runs to the Sports Complex. That bus runs daily out of the Disney-MGM Studios. It runs every 25 minutes or so. So you'll have to take the Studios bus then transfer to the WWoS bus to get there.
When you leave for Epcot, you will take the Studios bus back. Then you can either take the boat from the Studios to Epcot or there is an Epcot bus you can catch there.