UK light heavyweight Buatsi made a winning yet disappointing debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a tight ten-round contest at the Manchester venue.
But Parker found success, delivering effective single shots in a fight where the styles failed to mesh, with constant grabbing spoiling the fight.
Two judges had it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor said in the arena as he was met by disapproval from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers believed the challenger, thirty-one, deserved the win but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has slowed in recent times through management issues and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to narrowly win the better periods.
The crowd's patience wore thin during constant clinching, with Parker going down several times during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. However, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Arthur overcame Rea by close verdict in a outstanding all-Manchester contest to capture the European light-heavyweight belt.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells tolled in memory of Manchester's own Hatton, who passed away at age 46 in recently.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound faded, the quiet became a roar of "there's just one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the chin in the second round, rising shakily to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged soon, heavy swelling developing under his eye as the pair traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the verdict with judges scorecards of draw, 115-113 and wider gap, but the two athletes were persistent and courageous, all the qualities their inspiration the legend represented.
