UK light heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a tight ten-round contest at the Manchester venue.
But Parker found success, connecting with powerful single shots in a fight where the approaches failed to mesh, with frequent clinching disrupting the contest.
The scoring judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best display but what defines champions? They prevail," the victor stated in the ringside as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Some ringside observers believed the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second loss of his 28-bout career.
Buatsi Claims Victory in Uneventful Affair
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter ready to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective stanzas.
The audience's tolerance diminished amid regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a excellent all-Manchester contest to secure the European light-heavyweight title.
The arena grew hushed for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in honor of local hero Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the location since Hatton's passing. As the last bell ended, the silence became a roar of "only one Ricky Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was floored by a left hook directly to the face in the second round, rising shakily to his feet on the referee's count.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured soon, heavy swelling developing under his orbital area as the pair exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of draw, 115-113 and 115-112, but each competitor were determined and brave, everything their idol Hatton embodied.
