UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a contest where the approaches didn't complement each other, with constant grabbing marring the contest.
Two judges had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi stated in the arena as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, deserved the win but the British boxer experienced the second defeat of his 28-fight career.
Buatsi Secures Triumph in Slow Affair
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with neither fighter ready to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the continental championship.
The venue became quiet for a extremely emotional memorial before the fight as ten bells rang in memory of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The fighting within the ring matched the sentiment. The eventual winner was floored by a powerful punch squarely on the jaw in the early round, rising shakily to his position on the eight count.
But the traditional red attire of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged soon, significant bruising forming under his face as the pair landed hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor edged the result with scoring tallies of even score, close margin and clearer margin, but each competitor were relentless and full of heart, all the qualities their inspiration Hatton embodied.
