British light-heavyweight Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a contest where the styles never quite clicked, with constant grabbing marring the action.
The officials scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest showing but what defines champions? They win," Buatsi said in the ringside as he was faced boos from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Various analysts believed Parker, 31, deserved the win but the British boxer endured the second loss of his 28-fight career.
The Champion Secures Victory in Uneventful Match
His career development has plateaued in the past few years through contract problems and considerable time of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers willing to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who worked behind a tight guard to edge the more effective periods.
The spectators' acceptance diminished because of frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the European light heavyweight title.
The arena grew hushed for a extremely emotional memorial prior to the bout as ten bells rang in honor of the city's native Hatton, who succumbed at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the last bell faded, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising forming under his face as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the result with official scores of 114-114, 115-113 and clearer margin, but each competitor were persistent and courageous, everything their hero Hatton represented.
