He finished 1988 ranked No. 151 in the world rankings.
In April 1989, Pereira reached the Quarterfinals of the Tokyo Japan Open, beating No.21 ranked Andrés Gómez among others, before losing to number one ranked Ivan Lendl. In June, he beat world number three Stefan Edberg in straight sets in the first round of the Queens Club grass court tournament.
A few weeks later, in the first round of Wimbledon, he took world number one ranked Ivan Lendl to five sets before losing. Later that summer, he reached the Quarterfinals of the Grand Prix event at Montreal, the Canadian Open. There he beat No.10 ranked Tim Mayotte, before losing in three sets to number No.14 ranked Jay Berger. Pereira, at only 19 years of age, seemed to be establishing himself on the World Tennis Tour and finished 1989 ranked #121. However, for unknown reasons, Pereira's progress was stalled over the next three years. In 1990, he lost most of his matches in the first round of ATP level tournaments and finished the year ranked #238. In 1991 he did win the Lins and São Paulo-4 Challengers in back-to-back weeks, and was ranked No.146 at year's end. He won the Guarujá, Brazil Challenger in September 1992 and was ranked No.138 at the end of the year. In 1993, Pereira began to compete more frequently at the ATP tour level. At the U.S Open, he lost in four sets to world number seven Michael Chang. Incredibly, this marked only the third time Pereira had reached the second round of a Grand Slam tournament. He ended the year by defeating No.45 Aaron Krickstein in the first round at the Bermuda Challenger, but lost in the second round.
At the end of 1993, Pereira was ranked #141.
1994 marked a resurgence for Pereira. In March, he won the San Luis Potosí Challenger. At Wimbledon, he reached the second round where he lost a thrilling five set match to No.18 Andre Agassi. In September, Pereira beat Mauricio Hadad at the ATP Bogotá to register his first ATP tournament title. He closed out 1994 ranked #110. 1995 was a mixed bag for Pereira. In July, he annexed the Rio de Janeiro, Brazil Challenger title by defeating
Joao Culna-Silva in straight sets.
The next week at New Haven, he defeated No.39 MaliVai Washington in the second round, before bowing out top No.10 Marc Rosset.
At the U.S Open, Pereira reached the third round of a Grand Slam tournament for the first time, defeating No.57 Fabrice Santoro in a tight five setter in round one. He lost to Daniel Vacek in four sets in round three. At the end of the year, Nicolas was ranked #134. 1996 was another inconsistent year for Pereira. He started the year well in Doha by qualifying, then beating world number five Boris Becker 7–6 6–7 7–6 in a major upset in round two. He lost his next match. Pereira's somewhat baffling inconsistency was highlighted at the Qualifying tournament for the Australian Open, where he lost to unheralded Swede Patrik Fredriksson. Meanwhile, Becker, who had lost to Pereira only weeks earlier, won the Australian Open tournament. In March, Pereira again caused an upset when he beat world number one Thomas Muster in straight sets at the Masters Series tournament in Key Biscayne, Florida. However, he injured his knee during the match. Pereira lost in the third round to Stefan Edberg. After rehabilitating the knee, Nicolas returned at the French Open, in July, Pereira garnered his second career ATP title when he beat Grant Stafford on the grass courts at Newport, Rhode Island.
He reached his highest singles ATP-ranking on July 22 1996, when he became the number 74 player in the world. He represented Venezuela at the 1996 Summer Olympics in Atlanta, where he was defeated in the second round by India's Leander Paes. Pereira had mediocre results during the rest of 1996, and finished the year ranked #110. Nicolas, reportedly suffering from injuries, retired in September 1997 while ranked around world #400.