British light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round fight at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They win," Buatsi stated in the ringside as he was greeted with boos from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Various analysts thought the challenger, 31, deserved the victory but the contender suffered the second loss of his 28-fight career.
Buatsi Earns Win in Dull Encounter
His career development has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner rounds.
The crowd's patience decreased amid constant clinching, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but multiple periods were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by split-decision in a outstanding local rivalry contest to capture the continental title.
The venue fell silent for a deeply poignant tribute before the fight as 10 bells tolled in honor of the city's native Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell ended, the quiet gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a significant blow squarely on the jaw in the early round, rising shakily to his feet on the count of eight.
But the red-colored attire of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up early, significant bruising developing under his eye as the pair exchanged hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over 12 rounds.
The victor narrowly won the result with official scores of even score, narrow lead and clearer margin, but both fighters were relentless and courageous, exactly what their inspiration the legend represented.
