[6] On April 30, 1980, Mancini defeated Bobby Sparks with a knockout at 1:28 in the first round for the regional Ohio State Lightweight title.

On May 8, 1982, in a match held at The Aladdin in Las Vegas, he challenged the new World Boxing Association lightweight champion, Arturo Frias.

After many unanswered blows, referee Richard Greene stopped the fight at 2:54 in the first round, and the Mancini family finally had a world champion.

[8] The week after his death, the cover of Sports Illustrated magazine showed Mancini and Kim battling, under the title "Tragedy in the Ring".

In addition, Kim's mother died by suicide three months after the fight, and the bout's referee, Richard Green, killed himself in July 1983.

First, on September 15, 1983, he beat Peruvian challenger Orlando Romero by a knockout in nine rounds at Madison Square Garden to achieve a lifelong dream of fighting in that building, and then after a November 25 tune-up bout in which he defeated Johnny Torres by first-round knockout in his return to the Caesar's Palace hotel in Las Vegas, in January 1984, in a bout with former world champion Bobby Chacon, which was broadcast on HBO, Mancini defeated Chacon when referee Richard Steele stopped the fight in the third round with blood dripping from Chacon's left eye at Reno, Nevada.

[11] In June 1984, Mancini, still recovering from the emotional trauma of Kim's death, fought Livingstone Bramble to defend his title in Buffalo, New York.

[12] Mancini lost the title, but not before a fierce effort that resulted in an overnight stay at Millard Fillmore Hospital and 71 stitches around one eye.

[14] His next attempt came in March 1989, when he lost to Héctor 'Macho' Camacho in a split decision,[15] Mancini had one final fight in April 1992, against former lightweight champion Greg Haugen.

[17] The former champion was able to keep 75 percent of his $12 million in purse money, which enabled him to pursue a broad range of interests in retirement.

He appeared in the quirky 1994 comedy The Search for One-eye Jimmy, in David Mamet's MMA film Redbelt, and in the 2000 remake Body and Soul.

The documentary film featured his hometown friend, actor Ed O'Neill, and also included Jim Cummings, Kelly Pavlik, Jay Williams, Andrea Wood, and Mancini himself, among many other Youngstown natives and locals.

[19] Mancini has a son also named Ray who appeared in the YouTube reality series SummerBreak, in which Manicini also had a guest role.