UK light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a match where the techniques didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi said in the ringside as he was met by disapproval from the spectators.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought the challenger, 31, deserved the decision but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
The Champion Secures Victory in Dull Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the more effective periods.
The crowd's patience diminished during constant clinching, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur beat Rea by divided decision in a terrific local rivalry battle to capture the continental championship.
The venue fell silent for a extremely emotional homage prior to the bout as a bell ceremony tolled in remembrance of the city's native Hatton, who died aged 46 in September.
It was the first major televised fight night in the location since Hatton's death. As the final chime disappeared, the stillness gave way to a chant of "there's only one Hatton".
The fighting within the ring equaled the emotion. Arthur was floored by a significant blow squarely on the jaw in the early round, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up quickly, heavy swelling forming under his eye as the duo landed punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor narrowly won the result with scoring tallies of even score, narrow lead and 115-112, but both fighters were persistent and full of heart, exactly what their idol the legend stood for.
