UK light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight 10-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a fight where the styles failed to mesh, with constant grabbing spoiling the action.
The scoring judges judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," the victor stated in the arena as he was met by disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, merited the decision but the British boxer endured the second loss of his 28-match professional journey.
The Champion Secures Triumph in Dull Affair
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with the two boxers prepared to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who operated with a solid defense to narrowly win the cleaner stanzas.
The crowd's patience diminished amid constant clinching, with Parker going down various instances during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by close verdict in a excellent local rivalry contest to win the European light heavyweight belt.
The arena grew hushed for a extremely emotional memorial ahead of the contest as ten bells sounded in honor of the city's native Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime faded, the silence transitioned to a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the feeling. Arthur was sent to the canvas by a significant blow flush on the jaw in the second round, standing uncertainly to his position on the referee's count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the verdict with official scores of even score, narrow lead and wider gap, but the two athletes were determined and full of heart, everything their inspiration Hatton stood for.
