UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a close ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a match where the styles failed to mesh, with frequent clinching spoiling the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," the victor said in the arena as he was met by boos from the spectators.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the contender suffered the second setback of his 28-match career.
Buatsi Secures Victory in Slow Affair
His career development has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who utilized a protective stance to barely take the more effective periods.
The crowd's patience decreased amid regular grabbing, with Parker going down various instances during clinches.
Parker closed well, but many rounds were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Arthur overcame Rea by divided decision in a excellent local rivalry battle to capture the European light heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in honor of the city's native Hatton, who passed away 46 years old in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound ended, the silence gave way to a roar of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the face in the early round, rising shakily to his position on the referee's count.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, heavy swelling appearing under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the decision with scoring tallies of 114-114, close margin and 115-112, but both fighters were determined and full of heart, all the qualities their inspiration the legend represented.
