UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a close ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a fight where the approaches didn't complement each other, with constant grabbing spoiling the fight.
Two judges scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best performance but what defines champions? They succeed," the victor commented in the ring as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts thought the challenger, thirty-one, merited the win but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Claims Win in Dull Match
The fighter's advancement has slowed in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors prepared to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to edge the more effective periods.
The spectators' acceptance wore thin during regular grabbing, with Parker slipping to the canvas several times during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the European light-heavyweight title.
The arena grew hushed for a extremely emotional memorial ahead of the contest as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed 46 years old in September.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound ended, the stillness gave way to a roar of "only one Hatton".
The action during the bout reflected the emotion. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured early, heavy swelling forming under his face as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the verdict with official scores of 114-114, 115-113 and 115-112, but each competitor were determined and brave, all the qualities their inspiration the legend embodied.
