UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round contest at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a contest where the styles never quite clicked, with excessive holding marring the contest.
The scoring judges had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They prevail," the victor stated in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the win but the Derbyshire fighter endured the second loss of his 28-match career.
The Champion Secures Win in Slow Match
Buatsi's progress has plateaued in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter prepared to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance diminished because of constant clinching, with Parker slipping to the canvas various instances during grappling.
Parker closed well, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester contest to capture the European light heavyweight title.
The venue became quiet for a extremely emotional tribute ahead of the contest as 10 bells sounded in honor of Manchester's own Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The action within the ring equaled the feeling. Arthur was floored by a powerful punch directly to the chin in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was injured quickly, significant bruising developing under his face as the duo traded punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over the full distance.
Arthur edged the verdict with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and courageous, everything their hero Hatton stood for.
