British light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a fight where the approaches didn't complement each other, with excessive holding marring the action.
Two judges judged it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Several boxing experts thought Parker, thirty-one, deserved the victory but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Earns Victory in Dull Match
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors willing to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who utilized a tight guard to edge the more effective stanzas.
The audience's tolerance decreased because of constant clinching, with Parker falling to the floor various instances during close exchanges.
The underdog closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a terrific Manchester vs Manchester contest to capture the continental championship.
The venue became quiet for a extremely emotional tribute before the fight as ten bells sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound ended, the silence gave way to a shout of "there's just one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook directly to the face in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged early, heavy swelling forming under his face as the duo landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over the full distance.
The victor barely secured the result with scoring tallies of even score, close margin and 115-112, but both fighters were relentless and courageous, exactly what their hero Hatton stood for.
