British light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight ten-round contest at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a contest where the styles failed to mesh, with constant grabbing spoiling the action.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Various analysts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second loss of his 28-match career.
Buatsi Claims Win in Slow Affair
Buatsi's progress has plateaued in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to take risks in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to barely take the cleaner stanzas.
The spectators' acceptance diminished because of constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Arthur defeated Rea by close verdict in a terrific all-Manchester fight to secure the continental title.
The arena became quiet for a extremely emotional tribute prior to the bout as ten bells tolled in memory of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime faded, the silence gave way to a shout of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was floored by a significant blow flush on the face in the early round, rising shakily to his feet on the referee's count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was damaged quickly, noticeable damage appearing under his orbital area as the duo traded powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of draw, close margin and 115-112, but both fighters were determined and courageous, everything their idol Hatton stood for.
