British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a match where the approaches failed to mesh, with constant grabbing spoiling the fight.
The officials scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," the victor commented in the ring as he was met by negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Various analysts thought the challenger, 31, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-bout career.
Buatsi Earns Victory in Slow Match
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under fresh management.
He started carefully, with both competitors willing to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to edge the more effective stanzas.
The crowd's patience decreased during regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog closed well, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to capture the continental championship.
The stadium became quiet for a profoundly moving tribute prior to the bout as ten bells sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised fight night in the location since the passing of Hatton. As the last bell ended, the quiet became a chant of "there's just one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was floored by a significant blow squarely on the face in the early round, rising shakily to his footing on the count of eight.
But the traditional red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, heavy swelling forming under his face as the pair traded powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the verdict with judges scorecards of 114-114, close margin and 115-112, but the two athletes were persistent and full of heart, everything their inspiration the legend stood for.
