UK light heavyweight Buatsi made a winning yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But Parker found success, landing some telling clean blows in a match where the techniques never quite clicked, with constant grabbing spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," Buatsi stated in the ring as he was greeted with boos from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts believed Parker, 31, should have been awarded the decision but the contender suffered the second loss of his 28-bout professional journey.
The Champion Claims Victory in Dull Match
His career development has slowed in recent times through management issues and considerable time of lack of fights.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a last chance - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who utilized a solid defense to edge the more effective rounds.
The spectators' acceptance wore thin amid frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Arthur overcame Rea by divided decision in a excellent local rivalry battle to capture the European light-heavyweight title.
The arena became quiet for a extremely emotional homage prior to the bout as 10 bells tolled in honor of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the final chime disappeared, the quiet became a roar of "only one Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a powerful punch directly to the chin in the early round, rising shakily to his feet on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged soon, noticeable damage developing under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
The victor barely secured the decision with judges scorecards of draw, close margin and 115-112, but each competitor were persistent and courageous, exactly what their idol Hatton embodied.
