British light heavyweight Buatsi secured a victory yet disappointing debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a fight where the approaches didn't complement each other, with constant grabbing spoiling the contest.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," the victor stated in the arena as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Various analysts thought the challenger, 31, merited the victory but the British boxer experienced the second setback of his 28-bout professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has slowed in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under recent support.
He started carefully, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective rounds.
The spectators' acceptance diminished during constant clinching, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a terrific local rivalry battle to secure the continental championship.
The venue grew hushed for a extremely emotional memorial ahead of the contest as ten bells rang in honor of local hero Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a roar of "there's just one Hatton".
The action inside the ropes equaled the feeling. Arthur was knocked down by a significant blow directly to the face in the initial stage, rising shakily to his footing on the eight count.
But the traditional red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
Arthur barely secured the verdict with judges scorecards of draw, 115-113 and clearer margin, but each competitor were determined and full of heart, all the qualities their hero the legend embodied.
