UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the styles failed to mesh, with frequent clinching marring the action.
The officials had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the ring as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers felt Parker, thirty-one, deserved the decision but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Match
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective periods.
The crowd's patience diminished during regular grabbing, with the challenger falling to the floor multiple occasions during close exchanges.
Parker closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Motivates All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester battle to secure the European light heavyweight title.
The stadium grew hushed for a profoundly moving homage ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime ended, the quiet transitioned to a shout of "there's only one Hatton".
The fighting during the bout matched the sentiment. The eventual winner was knocked down by a left hook directly to the face in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising developing under his face as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the decision with scoring tallies of draw, close margin and wider gap, but both fighters were relentless and courageous, exactly what their hero the legend stood for.
