UK light-heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round bout at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a match where the approaches never quite clicked, with excessive holding marring the action.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," Buatsi said in the arena as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Secures Triumph in Uneventful Affair
His career development has plateaued in recent times through contract problems and considerable time of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to barely take the better stanzas.
The audience's tolerance wore thin during constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to secure the continental title.
The venue became quiet for a extremely emotional tribute ahead of the contest as ten bells tolled in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised fight night in the urban center since Hatton's death. As the last bell ended, the stillness gave way to a roar of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was floored by a powerful punch flush on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was injured early, noticeable damage appearing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were determined and courageous, exactly what their idol Hatton embodied.
