UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling clean blows in a contest where the approaches didn't complement each other, with frequent clinching marring the action.
The officials had it 96-94 to the winner, with the third a even score.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi commented in the ring as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the win but the contender experienced the second loss of his 28-fight professional journey.
The Champion Secures Triumph in Dull Affair
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the cleaner periods.
The spectators' acceptance decreased because of regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester battle to secure the European light heavyweight belt.
The stadium grew hushed for a deeply poignant homage before the fight as 10 bells sounded in honor of local hero Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell faded, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was floored by a significant blow directly to the face in the early round, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured quickly, significant bruising appearing under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the result with judges scorecards of draw, narrow lead and 115-112, but the two athletes were persistent and brave, all the qualities their inspiration the legend stood for.
