British light heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight ten-round fight at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a match where the styles failed to mesh, with constant grabbing spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my greatest showing but what defines champions? They prevail," the victor commented in the ring as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who utilized a tight guard to edge the more effective stanzas.
The spectators' acceptance decreased because of constant clinching, with Parker falling to the floor various instances during grappling.
The underdog closed well, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Arthur beat Rea by split-decision in a excellent all-Manchester battle to capture the European light heavyweight title.
The arena became quiet for a profoundly moving memorial prior to the bout as 10 bells sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime faded, the quiet became a shout of "only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the face in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged soon, significant bruising developing under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of draw, close margin and wider gap, but both fighters were persistent and brave, all the qualities their inspiration the legend stood for.
