UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the approaches never quite clicked, with frequent clinching marring the contest.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what do champions do? They win," Buatsi stated in the ring as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Various analysts thought the challenger, 31, deserved the win but the contender experienced the second loss of his 28-match professional journey.
Buatsi Claims Victory in Slow Encounter
Buatsi's progress has plateaued in recent times through management issues and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers ready to take risks in a cagey early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who utilized a solid defense to barely take the better stanzas.
The spectators' acceptance decreased amid constant clinching, with Parker falling to the floor various instances during clinches.
The underdog closed well, but many rounds were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a terrific all-Manchester fight to win the continental title.
The arena fell silent for a extremely emotional homage before the fight as 10 bells rang in memory of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound ended, the stillness became a roar of "only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was floored by a powerful punch squarely on the jaw in the second round, standing uncertainly to his footing on the eight count.
But the traditional red equipment of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his face as the fighters landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over twelve rounds.
Arthur edged the result with official scores of draw, close margin and clearer margin, but the two athletes were persistent and full of heart, exactly what their hero the legend embodied.
