I would also recommend parking at Mandalay Bay Parking. https://park.parkmobile.io/nv/las-vegas/mandalay-bay-events-center
However, be sure that you enter the parking garage on the west side of Mandalay Bay coming up from the south on Frank Sinatra Drive. It is a south turn off of Russell Rd that does a loop back north under Russell Rd. Be sure you take this loop!
Mandalay Bay Road will be closed (that is the road you walk over the freeway to Allegiant Stadium) and you will not be able to get to the parking any other way. If you follow map directions, it will not know that Mandalay Bay Road is closed and you could spend hours in traffic trying to get to the correct parking entrance (off of Frank Sinatra Drive) and miss part of the game.
My $0.02.