UK light-heavyweight Buatsi made a winning yet disappointing debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round contest at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi stated in the ring as he was faced negative reactions from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts thought Parker, 31, deserved the decision but the British boxer suffered the second defeat of his 28-bout professional journey.
The Champion Claims Triumph in Uneventful Match
Buatsi's progress has slowed in the past few years through management issues and long spells of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under recent support.
He began cautiously, with both competitors ready to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to narrowly win the better rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down various instances during clinches.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester battle to capture the European light-heavyweight championship.
The arena became quiet for a deeply poignant memorial ahead of the contest as ten bells sounded in remembrance of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a left hook flush on the chin in the second round, rising shakily to his feet on the count of eight.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up soon, noticeable damage forming under his orbital area as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the verdict with judges scorecards of draw, close margin and clearer margin, but both fighters were determined and full of heart, all the qualities their idol the legend represented.
