UK light-heavyweight Joshua Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close ten-round contest at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a fight where the techniques failed to mesh, with constant grabbing disrupting the contest.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They win," Buatsi said in the ring as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, should have been awarded the win but the British boxer suffered the second setback of his 28-match professional journey.
Buatsi Claims Victory in Dull Encounter
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who utilized a solid defense to narrowly win the cleaner periods.
The audience's tolerance decreased because of frequent holding, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester contest to win the European light-heavyweight belt.
The arena became quiet for a deeply poignant memorial prior to the bout as ten bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell disappeared, the stillness gave way to a chant of "there's only one Ricky Hatton".
The action within the ring reflected the emotion. Arthur was floored by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, significant bruising forming under his orbital area as the duo exchanged punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur barely secured the result with scoring tallies of 114-114, close margin and wider gap, but each competitor were relentless and brave, everything their inspiration the legend embodied.
