British light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a match where the techniques didn't complement each other, with frequent clinching disrupting the contest.
The scoring judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best performance but what do champions do? They win," Buatsi commented in the ringside as he was faced disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Dull Affair
His career development has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who operated with a tight guard to barely take the cleaner rounds.
The spectators' acceptance wore thin because of constant clinching, with the challenger falling to the floor several times during close exchanges.
The underdog closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a outstanding local rivalry battle to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as ten bells tolled in remembrance of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the urban center since Hatton's passing. As the last bell disappeared, the stillness became a shout of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. Arthur was floored by a left hook squarely on the chin in the early round, getting up unsteadily to his position on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up soon, noticeable damage developing under his orbital area as the pair exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the action hardly diminished over 12 rounds.
The victor edged the verdict with official scores of 114-114, close margin and 115-112, but both fighters were determined and full of heart, all the qualities their idol the legend represented.
