UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a match where the approaches failed to mesh, with frequent clinching marring the fight.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi said in the ring as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, thirty-one, merited the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Secures Win in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a tight guard to barely take the cleaner periods.
The audience's tolerance decreased during frequent holding, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight championship.
The arena grew hushed for a deeply poignant homage prior to the bout as a bell ceremony tolled in remembrance of the city's native Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the urban center since Hatton's passing. As the last bell faded, the quiet became a shout of "there's just one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was injured quickly, noticeable damage developing under his orbital area as the pair traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of draw, 115-113 and wider gap, but the two athletes were determined and brave, exactly what their hero Hatton stood for.
