UK light heavyweight Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective clean blows in a contest where the techniques never quite clicked, with frequent clinching disrupting the contest.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my finest display but what defines champions? They prevail," the victor commented in the arena as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second setback of his 28-fight professional journey.
The Champion Secures Victory in Uneventful Affair
Buatsi's progress has plateaued in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a calculated opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to barely take the better periods.
The crowd's patience wore thin during frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Fuels Manchester Derby Fight
In the secondary fight, Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the European light heavyweight championship.
The stadium became quiet for a deeply poignant memorial prior to the bout as ten bells tolled in remembrance of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised match card in the city since Hatton's death. As the concluding sound disappeared, the quiet became a shout of "there's just one Hatton".
The action within the ring matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, rising shakily to his feet on the eight count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up quickly, heavy swelling forming under his orbital area as the pair traded powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, close margin and wider gap, but each competitor were persistent and brave, exactly what their idol the legend stood for.
