British light heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing 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 close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a match where the styles never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi stated in the ring as he was faced disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second loss of his 28-match professional journey.
The Champion Claims Win in Dull Match
The fighter's advancement has stalled in recent years through contract problems and long spells of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a tentative early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner periods.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a outstanding local rivalry battle to win the continental title.
The venue became quiet for a profoundly moving tribute prior to the bout as ten bells rang in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the last bell ended, the silence transitioned to a chant of "there's only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was knocked down by a powerful punch flush on the chin in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, noticeable damage developing under his eye as the duo traded powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the verdict with scoring tallies of 114-114, close margin and wider gap, but both fighters were relentless and courageous, all the qualities their hero Hatton stood for.
