UK light heavyweight Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a match where the techniques never quite clicked, with frequent clinching marring the action.
The officials had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts thought Parker, 31, merited the victory but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Secures Win in Dull Encounter
His career development has plateaued in recent times through management issues and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who operated with a tight guard to edge the more effective rounds.
The spectators' acceptance wore thin because of frequent holding, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. However, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur overcame Rea by split-decision in a excellent all-Manchester fight to win the continental belt.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as 10 bells sounded in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the last bell ended, the stillness gave way to a chant of "there's only one Hatton".
The fighting during the bout equaled the emotion. The eventual winner was floored by a significant blow squarely on the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the red-colored equipment of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was marked up early, significant bruising developing under his eye as the pair landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the verdict with official scores of 114-114, 115-113 and 115-112, but the two athletes were relentless and brave, all the qualities their hero Hatton stood for.
