UK light heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the styles failed to mesh, with constant grabbing disrupting the action.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They succeed," the victor commented in the arena as he was faced negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Various analysts believed the challenger, 31, should have been awarded the win but the British boxer endured the second defeat of his 28-match career.
Buatsi Secures Victory in Uneventful Encounter
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with the two boxers prepared to be aggressive in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to edge the better rounds.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester contest to win the continental championship.
The arena fell silent for a profoundly moving tribute ahead of the contest as ten bells rang in memory of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the concluding sound faded, the quiet gave way to a chant of "there's only one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was knocked down by a significant blow directly to the chin in the early round, rising shakily to his position on the referee's count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up soon, heavy swelling forming under his orbital area as the duo landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of 114-114, close margin and clearer margin, but the two athletes were determined and full of heart, everything their hero Hatton stood for.
