Nelson began 1988 by defeating Mario Martinez by a split decision over 12 rounds in Los Angeles to win the vacant WBC super featherweight title. Nelson was dropped in the 10the round of their encounter and the decision was not well received. He defended the title with a knockout in round nine against former world champ Lupe Suarez, and with a knockout in three over Sydney del Rovere.
He proceeded in 1989 by beating Martinez in a rematch, by knockout in round 12, and then fighting Jim McConnell with exactly the same result. The fight with McDonnell, fought in London, was considered one of the fights of the year by many boxing magazines, and McDonnell was widely praised by critics for his stand against Nelson. McDonnell suffered four knockdowns before the fight was stopped by referee Joe Cortez.
On 19 May 1990, Nelson tried to join the exclusive group of three division world champion boxers by challenging world lightweight champion Pernell Whitaker, but he was handed his second career loss when Whitaker won a 12 round unanimous decision to retain the title. For his next fight, he went to Australia to meet the former world Featherweight champion, Puerto Ricoís Juan Laporte. He beat Laporte by a decision in 12 to retain the world Jr. Lightweight title.
In 1991, he had only tow fights. In Spain, he beat Daniel Mustapha by a knockout in round four of a non-title bout, and then, in Las Vegas, he retained the title with a controversial draw against three weight world champion Jeff Fenech. Many ringside observers and boxing writers felt Fenech had deserved to win that night, and an immediate rematch was signed and set for 1 March 1992.
Back in Australia, Nelson defeated Fenech by a knockout in round eight of their sequel, and then he retained the title with a 12 round decision over former world champion Calvin Grove on 7 November.
On 20 February 1993, the world traveling champion defeated future world champion Gabriel Ruelas by decision in 12 in front of 120,000 fans (most of whom had come to watch Julio Cesar Chavez defend his world title against Greg Haugen in the eveningís main event) in Mexico. The 120,000 fan turnout was the largest ever for a boxing event. Then, on 10 September, he began his four fights series with future world champion Jesse James Leija by retaing the title with a draw as part of the Julio Cesar Chavez-Pernell Whitaker fightís undercard in San Antonio. Originally announced as a winner, Nelson found out minutes later when Leija was being interviewed that the correct outcome was a draw, giving Leija a rematch. The fightís announcer had accidentally mixed the scorecards and announced Melson the winner. Even though the decision was changed to draw, Nelson still kept his title.
On 7 May 1994, he and Leija met for the second time: That time around, the announcer was right when he announced Leija was winner and new world champion. That was Nelsonís only bout in 1994.
Leija quickly lost the title to Ruelas, who defended against Nelson on 1 December 1995, and Nelson recovered the title in his rematch with Ruelas by knocking him out in round five.
His first defense took place almost a year later, when he and Leija had their third bout. Nelson retained the title with a six round knockout. As had become his common practice, that was the only time Nelson fought in 1996.