UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close 10-round contest at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a contest where the techniques failed to mesh, with constant grabbing spoiling the action.
Two judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers felt Parker, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-match professional journey.
The Champion Secures Win in Uneventful Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a protective stance to edge the cleaner periods.
The crowd's patience decreased because of constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Arthur beat Rea by divided decision in a excellent local rivalry fight to win the European light-heavyweight title.
The stadium became quiet for a profoundly moving memorial prior to the bout as ten bells tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the last bell ended, the quiet became a shout of "there's only one Hatton".
The fighting within the ring equaled the sentiment. Arthur was sent to the canvas by a significant blow flush on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was injured quickly, significant bruising forming under his face as the pair exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the verdict with official scores of even score, 115-113 and 115-112, but each competitor were relentless and courageous, all the qualities their hero Hatton stood for.
