British light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a fight where the approaches didn't complement each other, with frequent clinching marring the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," the victor said in the ringside as he was faced disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts felt Parker, 31, deserved the victory but the British boxer suffered the second loss of his 28-bout professional journey.
Buatsi Earns Triumph in Dull Affair
The fighter's advancement has plateaued in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He started carefully, with the two boxers prepared 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 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the better periods.
The audience's tolerance wore thin during constant clinching, with the challenger falling to the floor various instances during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight belt.
The arena grew hushed for a deeply poignant tribute prior to the bout as ten bells sounded in honor of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a shout of "only one Hatton".
The competition inside the ropes matched the emotion. Arthur was sent to the canvas by a left hook directly to the chin in the initial stage, rising shakily to his position on the eight count.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged soon, heavy swelling appearing under his orbital area as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur edged the verdict with scoring tallies of draw, close margin and clearer margin, but both fighters were persistent and full of heart, everything their inspiration Hatton embodied.
