British light-heavyweight Joshua Buatsi earned a win yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the approaches didn't complement each other, with constant grabbing marring the action.
The scoring judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor said in the arena as he was greeted with disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the win but the contender experienced the second defeat of his 28-match career.
The Champion Claims Triumph in Slow Match
Buatsi's progress has slowed in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The spectators' acceptance wore thin amid regular grabbing, with the challenger going down various instances during clinches.
The underdog closed well, but many rounds were hard to judge. Although, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Fuels All-Manchester Battle
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding all-Manchester battle to secure the European light-heavyweight title.
The stadium became quiet for a deeply poignant memorial prior to the bout as ten bells tolled in remembrance of the city's native Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound ended, the stillness became a roar of "there's just one Ricky Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the face in the second round, rising shakily to his feet on the eight count.
But the traditional red equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured soon, heavy swelling appearing under his face as the pair traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, 115-113 and wider gap, but the two athletes were relentless and full of heart, all the qualities their inspiration the legend embodied.
