Rough day at the office for ex-UFC star Sage Northcutt -- who just got his face obliterated 30 seconds into his ONE Championship debut.
The 23-year-old was taking on Brazilian fighter Cosmo Alexandre in Singapore ... when just 25 seconds into the fight, things went bad for Sage.
Cosmo cracked the kid with a solid right -- immediately turning off Sage's lights and sending him crashing to the floor face first.
Cosmo Alexandre STARCHES Sage Northcutt in 30 seconds to spoil his much anticipated ONE debut ud83dude31 pic.