British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a match where the approaches never quite clicked, with frequent clinching disrupting the contest.
Two judges judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They succeed," Buatsi stated in the ringside as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought Parker, 31, merited the decision but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
The Champion Earns Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers ready to overcommit in a calculated early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to barely take the cleaner periods.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Fuels Local Rivalry Battle
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester battle to capture the European light-heavyweight belt.
The arena fell silent for a profoundly moving tribute ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Hatton, who died 46 years old in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the stillness gave way to a roar of "there's just one Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was damaged early, heavy swelling forming under his face as the fighters traded punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace hardly diminished over the full distance.
Arthur edged the verdict with scoring tallies of draw, close margin and 115-112, but each competitor were relentless and brave, everything their inspiration the legend embodied.
