British light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a fight where the techniques never quite clicked, with excessive holding marring the action.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," the victor said in the ring as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, merited the victory but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Victory in Slow Match
His career development has stalled in the past few years through contract problems and considerable time of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who operated with a solid defense to barely take the better stanzas.
The crowd's patience diminished because of frequent holding, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but many rounds were challenging to assess. However, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight title.
The arena grew hushed for a deeply poignant tribute ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the final chime faded, the quiet became a shout of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was knocked down by a powerful punch squarely on the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged early, significant bruising developing under his eye as the pair exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the result with official scores of even score, 115-113 and 115-112, but the two athletes were persistent and courageous, exactly what their hero the legend stood for.
