British light-heavyweight Buatsi earned a win yet disappointing start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a fight where the techniques failed to mesh, with excessive holding disrupting the contest.
The officials scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi commented in the ringside as he was faced negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the decision but the Derbyshire fighter suffered the second setback of his 28-bout career.
Buatsi Earns Victory in Uneventful Affair
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a solid defense to barely take the better periods.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur beat Rea by split-decision in a terrific all-Manchester fight to secure the continental title.
The stadium became quiet for a extremely emotional tribute before the fight as ten bells tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised fight night in the location since Hatton's passing. As the final chime ended, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring matched the emotion. Arthur was floored by a significant blow squarely on the chin in the early round, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up early, heavy swelling developing under his orbital area as the fighters exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor barely secured the decision with scoring tallies of draw, 115-113 and clearer margin, but both fighters were persistent and courageous, exactly what their inspiration the legend stood for.
