British light-heavyweight Buatsi made a winning yet underwhelming debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, delivering effective individual punches in a fight where the styles failed to mesh, with excessive holding spoiling the action.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," the victor said in the ringside as he was faced boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-match career.
The Champion Secures Triumph in Uneventful Match
Buatsi's progress has slowed in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the more effective periods.
The audience's tolerance wore thin during regular grabbing, with the challenger going down several times during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Hatton Homage Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester fight to win the continental championship.
The stadium grew hushed for a deeply poignant tribute prior to the bout as 10 bells sounded in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the silence became a roar of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his orbital area as the duo traded hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the verdict with scoring tallies of even score, close margin and clearer margin, but each competitor were persistent and courageous, all the qualities their idol Hatton stood for.
