British light-heavyweight Joshua Buatsi earned a win yet disappointing start to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker found success, delivering effective single shots in a contest where the techniques never quite clicked, with frequent clinching marring the contest.
The officials scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," the victor said in the arena as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second defeat of his 28-match professional journey.
Buatsi Secures Win in Uneventful Affair
The fighter's advancement has slowed in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to edge the more effective stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger falling to the floor various instances during grappling.
The underdog closed well, but many rounds were hard to judge. However, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester fight to secure the continental title.
The stadium became quiet for a extremely emotional homage prior to the bout as ten bells tolled in memory of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the final chime ended, the stillness gave way to a shout of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged soon, heavy swelling developing under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the result with scoring tallies of draw, close margin and clearer margin, but the two athletes were relentless and courageous, all the qualities their inspiration the legend stood for.
