British light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective clean blows in a contest where the approaches never quite clicked, with constant grabbing marring the action.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," the victor commented in the ring as he was greeted with boos from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, 31, merited the win but the contender suffered the second loss of his 28-fight career.
The Champion Secures Triumph in Uneventful Affair
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who operated with a solid defense to barely take the better rounds.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Arthur beat Bradley Rea by close verdict in a excellent all-Manchester contest to win the European light heavyweight belt.
The venue fell silent for a profoundly moving memorial ahead of the contest as ten bells rang in honor of local hero Hatton, who died at age 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound faded, the quiet became a roar of "there's only one Hatton".
The fighting during the bout equaled the sentiment. The eventual winner was knocked down by a significant blow directly to the chin in the second round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was injured soon, heavy swelling forming under his eye as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur narrowly won the decision with scoring tallies of 114-114, close margin and clearer margin, but both fighters were relentless and courageous, exactly what their idol the legend stood for.
