British light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive ten-round fight at the boxing arena.
But the challenger found success, connecting with powerful single shots in a fight where the approaches failed to mesh, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi said in the ringside as he was met by negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to earn a 20th career victory.
Various analysts believed Parker, 31, deserved the decision but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Slow Match
The fighter's advancement has plateaued in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who operated with a solid defense to narrowly win the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with Parker falling to the floor various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry contest to secure the European light-heavyweight belt.
The stadium became quiet for a profoundly moving tribute prior to the bout as 10 bells tolled in memory of local hero Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the last bell disappeared, the quiet gave way to a shout of "only one Ricky Hatton".
The competition within the ring equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the face in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was damaged soon, significant bruising appearing under his eye as the pair landed hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the result with scoring tallies of 114-114, 115-113 and 115-112, but both fighters were determined and courageous, all the qualities their idol Hatton embodied.
