British light heavyweight Joshua Buatsi earned a win yet disappointing start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a match where the approaches didn't complement each other, with constant grabbing spoiling the contest.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi said in the arena as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Several boxing experts believed the challenger, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Win in Uneventful Match
The fighter's advancement has slowed in recent times through promotional disputes and long spells of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with neither fighter prepared to overcommit in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the more effective stanzas.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester battle to win the continental belt.
The stadium fell silent for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in memory of local hero Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime faded, the quiet transitioned to a chant of "only one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a left hook directly to the chin in the early round, getting up unsteadily to his feet on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was marked up quickly, heavy swelling appearing under his orbital area as the duo landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
The victor narrowly won the result with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and full of heart, exactly what their idol the legend embodied.
