British light heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight 10-round bout at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the techniques never quite clicked, with excessive holding disrupting the contest.
Two judges scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my finest display but what do champions do? They succeed," Buatsi commented in the ring as he was met by boos from the spectators.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the win but the British boxer endured the second setback of his 28-match career.
Buatsi Earns Triumph in Dull Affair
Buatsi's progress has stalled in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to barely take the better periods.
The crowd's patience wore thin during regular grabbing, with the challenger going down multiple occasions during clinches.
Parker finished the stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a excellent all-Manchester contest to capture the continental championship.
The arena became quiet for a deeply poignant homage ahead of the contest as ten bells rang in memory of the city's native Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the concluding sound faded, the stillness gave way to a roar of "there's only one Ricky Hatton".
The competition within the ring reflected the emotion. Arthur was floored by a left hook flush on the chin in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured quickly, heavy swelling developing under his face as the pair landed hard punches.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the action hardly diminished over the full distance.
The victor narrowly won the result with judges scorecards of 114-114, close margin and 115-112, but both fighters were persistent and courageous, everything their hero the legend embodied.
