British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the techniques never quite clicked, with constant grabbing spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Various analysts believed the challenger, thirty-one, merited the win but the contender endured the second setback of his 28-fight career.
The Champion Secures Victory in Slow Encounter
The fighter's advancement has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who operated with a protective stance to edge the better periods.
The audience's tolerance wore thin amid constant clinching, with the challenger going down several times during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Contest
In the secondary fight, Arthur beat Rea by divided decision in a terrific all-Manchester battle to capture the European light heavyweight title.
The venue became quiet for a profoundly moving homage ahead of the contest as ten bells tolled in honor of the city's native Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a chant of "there's just one Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a powerful punch flush on the face in the second round, standing uncertainly to his position on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged early, significant bruising appearing under his eye as the pair exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the verdict with judges scorecards of even score, close margin and wider gap, but the two athletes were determined and courageous, all the qualities their idol Hatton stood for.
