British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a contest where the approaches never quite clicked, with constant grabbing disrupting the action.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what defines champions? They succeed," the victor stated in the ringside as he was met by disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-match career.
The Champion Secures Victory in Slow Match
His career development has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a tight guard to barely take the better periods.
The crowd's patience diminished amid constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight title.
The venue grew hushed for a deeply poignant homage prior to the bout as a bell ceremony sounded in memory of local hero Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell ended, the stillness became a shout of "there's only one Hatton".
The competition within the ring matched the emotion. Arthur was knocked down by a significant blow flush on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up early, heavy swelling appearing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor narrowly won the verdict with official scores of draw, close margin and 115-112, but each competitor were relentless and courageous, exactly what their idol Hatton embodied.
