If ya think Bob Costas is bitter about Mike Tirico holding his old seat in Pyeongchang, think again -- 'cause Bob tells TMZ Sports Mike's doing "a great job" with Olympics coverage.
Costas wasn't keen on talking gun control (remember his Sunday Night Football speech?) when we got him out in Bev Hills -- but he was as friendly as ever to our guy, and seemed legitimately happy for his NBC successor.
There were some rumors that Bob's passing of the torch might not have been entirely up to him ... but either way, looks like things are all Gucci.
Guessing it helps that he's in L.A. instead of freezing his ass off.
FYI, Costas began hosting Olympics coverage for NBC back in '92 and hadn't missed the Games until he hung it up this year.