UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a contest where the styles didn't complement each other, with frequent clinching disrupting the fight.
Two judges scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi commented in the ring as he was met by boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the win but the Derbyshire fighter endured the second loss of his 28-match professional journey.
Buatsi Claims Win in Uneventful Affair
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a tentative early stages.
Parker, whose single earlier setback 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 light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The crowd's patience diminished because of frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent local rivalry battle to secure the European light heavyweight belt.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the silence became a roar of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. Arthur was floored by a powerful punch squarely on the jaw in the early round, standing uncertainly to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged quickly, heavy swelling forming under his orbital area as the fighters traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor narrowly won the result with judges scorecards of 114-114, close margin and clearer margin, but each competitor were persistent and courageous, all the qualities their idol the legend stood for.
