Mayweather expected to be around $200 million wealthier, taking his career earnings to around $1 billion.
McGregor, who was an unemployed former plumber four years ago before emerging as one of the biggest stars of the Ultimate Fighting Championship, is expected to earn around $100 million.
If pay-per-view television targets are met, the fight could become the most lucrative in history.
The start of the bout had been delayed by several minutes as anticipation built to fever pitch and television providers struggled to cope with the surge in demand from pay-per-view customers.
(Source: CNBC YouTube channel)