UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the styles never quite clicked, with frequent clinching spoiling the contest.
The officials had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what do champions do? They prevail," Buatsi commented in the arena as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the win but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
His career development has slowed in recent times through contract problems and extended periods of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who operated with a solid defense to barely take the cleaner stanzas.
The spectators' acceptance decreased because of frequent holding, with the challenger going down various instances during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
In the secondary fight, Arthur beat Rea by close verdict in a terrific local rivalry contest to capture the European light heavyweight belt.
The arena grew hushed for a profoundly moving tribute before the fight as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the last bell ended, the silence became a chant of "only one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, significant bruising appearing under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and full of heart, all the qualities their hero the legend stood for.
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