British light-heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a fight where the approaches didn't complement each other, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi commented in the ringside as he was met by negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Some ringside observers believed the challenger, thirty-one, should have been awarded the victory but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Secures Triumph in Dull Match
Buatsi's progress has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to edge the better stanzas.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor various instances during grappling.
Parker closed well, but several stanzas were hard to judge. However, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a terrific local rivalry fight to secure the continental title.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells rang in memory of the city's native Ricky Hatton, who died 46 years old in last month.
It was the first major televised fight night in the city since Hatton's passing. As the last bell disappeared, the stillness became a roar of "there's just one Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was floored by a left hook directly to the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was injured soon, noticeable damage appearing under his eye as the pair traded hard punches.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the decision with scoring tallies of 114-114, narrow lead and wider gap, but each competitor were persistent and courageous, exactly what their idol the legend represented.
