British light-heavyweight Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a tight 10-round bout at the boxing arena.
But Parker had his moments, delivering effective single shots in a fight where the styles never quite clicked, with frequent clinching spoiling the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi said in the ring as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the win but the contender experienced the second setback of his 28-match career.
The Champion Secures Triumph in Dull Match
His career development has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who utilized a solid defense to edge the better periods.
The crowd's patience decreased because of regular grabbing, with the challenger going down several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight belt.
The stadium became quiet for a extremely emotional homage prior to the bout as 10 bells tolled in honor of local hero Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the final chime faded, the quiet gave way to a chant of "there's only one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up quickly, noticeable damage developing under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the decision with scoring tallies of draw, close margin and clearer margin, but the two athletes were determined and brave, everything their hero the legend represented.
