UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a contest where the approaches failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," Buatsi said in the ringside as he was faced boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, deserved the decision but the British boxer endured the second setback of his 28-bout career.
Buatsi Claims Triumph in Slow Encounter
Buatsi's progress has plateaued in recent years through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers prepared to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner rounds.
The spectators' acceptance decreased because of regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur beat Bradley Rea by divided decision in a excellent all-Manchester fight to win the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute before the fight as 10 bells rang in memory of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting during the bout equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was damaged early, heavy swelling developing under his face as the fighters traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
The victor edged the result with scoring tallies of 114-114, narrow lead and clearer margin, but the two athletes were relentless and courageous, exactly what their idol the legend stood for.
