The decision to open the main WrestleMania card with Brock Lesnar vs. Seth Rollins was only made at around 5:30 PM ET last night, after the Kickoff show had already started, according to Dave Meltzer on Wrestling Observer Radio.
It’s not known what was originally supposed to open the show. Paul Heyman ended up coming out and saying that if Lesnar wasn’t closing the show, he and Heyman weren’t going to stick around all night, so the match was happening right now, and it led to a very hot open.
Heyman marched out past Hulk Hogan and Alexa Bliss, who did a brief opening segment together. According to Meltzer, Hogan legitimately had no idea what was going on when Heyman came out, since that wasn’t part of the original plan and it was such a late change, and apparently no one told Hogan.