UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger found success, landing some telling clean blows in a match where the styles didn't complement each other, with constant grabbing marring the contest.
Two judges scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," the victor stated in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed Parker, 31, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-match career.
Buatsi Earns Triumph in Dull Encounter
The fighter's advancement has plateaued in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who operated with a solid defense to barely take the better periods.
The audience's tolerance decreased amid constant clinching, with Parker going down various instances during clinches.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The stadium became quiet for a profoundly moving homage before the fight as a bell ceremony rang in honor of the city's native Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the final chime disappeared, the stillness became a shout of "only one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured early, heavy swelling forming under his eye as the fighters traded punishing blows.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
Arthur barely secured the decision with scoring tallies of draw, close margin and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration Hatton represented.
