UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful single shots in a contest where the styles never quite clicked, with excessive holding spoiling the contest.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They prevail," Buatsi said in the ringside as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, merited the victory but the British boxer experienced the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Uneventful Affair
The fighter's advancement has stalled in recent years through management issues and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under new promotional backing.
He started carefully, with neither fighter willing to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to narrowly win the more effective rounds.
The crowd's patience wore thin amid frequent holding, with the challenger going down various instances during clinches.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur beat Rea by divided decision in a terrific Manchester vs Manchester battle to win the European light-heavyweight belt.
The stadium fell silent for a extremely emotional tribute before the fight as a bell ceremony tolled in memory of Manchester's own Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the city since Hatton's passing. As the last bell disappeared, the silence transitioned to a shout of "there's only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a significant blow flush on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was marked up quickly, heavy swelling developing under his eye as the fighters landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the decision with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were determined and courageous, exactly what their inspiration Hatton stood for.
