The two boxers were both courtside – directly across from one another – for Miami Heat???s NBA clash with Milwaukee Bucks, which the Bucks won 109-102.
Mayweather went over to Pacquiao at half-time, the men shook hands and chatted briefly, then exchanged phone numbers.
A fight between the pair, which could be worth around ??160m, has been mooted for May 2 and Pacquiao suggested after their meeting that they could now negotiate directly about meeting in the ring.
“He gave his number to me and said we will communicate with each other,” said Pacquiao.
American Mayweather, the WBA and WBC welterweight champion, has not lost in 47 fights, while Filipino Pacquiao, the WBO welterweight title-holder, is 57-5-2 in his career.
It appears to have been a coincidence that the pair met at the Heat game after Pacquiao, who was in London last week, decided to watch it after having his flight cancelled due to the severe winter storm that has hit the United States in recent days. He had been serving as one of the judges in the Miss Universe pageant at Florida International University.
Mayweather has been a regular courtside attendee at Heat games for several years.