British light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the techniques didn't complement each other, with constant grabbing disrupting the contest.
Two judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They succeed," the victor commented in the arena as he was met by disapproval from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the win but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Slow Encounter
His career development has slowed in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to narrowly win the better periods.
The spectators' acceptance diminished during regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester contest to secure the European light-heavyweight title.
The arena became quiet for a profoundly moving memorial prior to the bout as ten bells sounded in memory of Manchester's own Ricky Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime ended, the silence transitioned to a shout of "only one Ricky Hatton".
The competition during the bout matched the sentiment. The eventual winner was knocked down by a powerful punch flush on the chin in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was marked up early, heavy swelling developing under his face as the fighters traded powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the pace hardly diminished over the full distance.
The victor edged the decision with scoring tallies of even score, 115-113 and clearer margin, but the two athletes were determined and courageous, all the qualities their hero the legend embodied.
