British light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round contest at the boxing arena.
But Parker found success, delivering effective clean blows in a contest where the approaches failed to mesh, with excessive holding spoiling the contest.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They win," the victor stated in the ring as he was met by negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the British boxer experienced the second loss of his 28-bout professional journey.
Buatsi Earns Victory in Dull Encounter
His career development has stalled in recent times through management issues and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to realize his potential - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with both competitors ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to edge the better periods.
The crowd's patience wore thin because of frequent holding, with Parker going down various instances during clinches.
Parker closed well, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight championship.
The venue became quiet for a extremely emotional memorial before the fight as a bell ceremony sounded in remembrance of the city's native Hatton, who passed away aged 46 in recently.
It was the first major televised boxing event in the city since Hatton's death. As the final chime faded, the quiet became a chant of "only one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was floored by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red equipment of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, significant bruising developing under his orbital area as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over the full distance.
Arthur edged the verdict with official scores of 114-114, narrow lead and wider gap, but each competitor were relentless and courageous, all the qualities their idol the legend stood for.
