Buatsi, an Olympic bronze medallist in Rio in 2016, dominated the early stages then fended off a big comeback by Richards to claim a 116-112, 115-113, 115-113 unanimous verdict.
Bivol’s win over Alvarez had served to raise the reputation of Richards, the 32-year-old who suffered his only career defeat on points to Bivol last year.
But the strong and accurate Buatsi seized the advantage from the start and it took Richards until the fifth round to really begin to make any kind of impression.
Buatsi was strong and accurate but tended to find success in bursts, and Richards came on strong in the eighth round with a big right hand followed by a flurry that appeared to trouble the favourite.
Richards landed more rights in the ninth but Buatsi continued to shade the cleaner work and pair continued to exchange hard blows in an exciting finale before Buatsi’s arm was eventually raised.