Peterson had been preparing for his rematch with Amir Khan last summer, but failed a drugs test and was handed a subsequent ban, although he kept one of his world titles.
In his return yesterday evening, the 29-year-old began shakily, getting tagged by Holt often.
He dropped the challenger in round four with a powerful right and dominated the fight thereafter, before completing an eighth-round stoppage.
"I spent a lot of energy trying to get him out," Peterson told ESPN afterwards.
"I have to look at the tape [to see how I performed]. I always give myself a bad grade when I fight.
"Right now, I got the win, so I'll say I did a good job."
Peterson improved his record to 36 wins, one defeat and a single draw.