UK light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker had his moments, landing some telling clean blows in a contest where the techniques didn't complement each other, with constant grabbing disrupting the action.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They succeed," the victor stated in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to earn a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the win but the contender experienced the second loss of his 28-bout career.
Buatsi Claims Win in Uneventful Match
His career development has stalled in recent times through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the better stanzas.
The crowd's patience wore thin during constant clinching, with the challenger falling to the floor multiple occasions during clinches.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Memorial Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a outstanding all-Manchester fight to secure the European light-heavyweight championship.
The venue became quiet for a profoundly moving homage ahead of the contest as ten bells rang in honor of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound faded, the silence became a shout of "there's only one Ricky Hatton".
The action during the bout matched the emotion. Arthur was knocked down by a left hook squarely on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged soon, heavy swelling developing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the action seldom decreased over the full distance.
Arthur barely secured the result with judges scorecards of even score, close margin and 115-112, but the two athletes were relentless and courageous, everything their hero the legend embodied.
