British light-heavyweight Joshua Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the techniques failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best performance but how do champions respond? They succeed," the victor commented in the arena as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the contender experienced the second defeat of his 28-bout career.
Buatsi Secures Victory in Uneventful Affair
The fighter's advancement has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He started carefully, with both competitors willing to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who worked behind a tight guard to edge the more effective periods.
The spectators' acceptance diminished during frequent holding, with Parker going down multiple occasions during clinches.
Parker closed well, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by split-decision in a terrific local rivalry fight to capture the European light heavyweight championship.
The venue fell silent for a deeply poignant homage ahead of the contest as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime ended, the quiet transitioned to a shout of "only one Hatton".
The action inside the ropes reflected the sentiment. Arthur was knocked down by a powerful punch directly to the jaw in the initial stage, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, noticeable damage forming under his eye as the duo traded hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were relentless and brave, exactly what their idol Hatton represented.
