He is also known as Charlito ("Little Charlie") because his father had the same name and was also a gifted tennis player, being the champion of Puerto Rico six times in the 1950s. Pasarell was a prestigious junior and first appeared on the cover of "World Tennis Magazine" at the age of 11 in 1955. He won over half dozen Orange Bowl titles and five US junior titles including the US juniors in singles and doubles with
Clark Graebner in 1961. He first appeared in the U.S. Championships at
Forest Hills in 1960 and was first ranked nationally that year. In 1962, he played at the
Caribe Hilton Championships in San Juan, Puerto Rico. This was arguably the biggest tournament in the whole of Central, Caribbean and South America. Charlie was only just 18 and beat U.S. No. 7
Ron Holmberg, followed by Mexican No. 1,
Mario Llamas, 6–0, 6–0 in the quarterfinals (avenging a similar defeat of his 14-year-old brother Stanley earlier in the tournament). In the semifinals, Charlie met Rod Laver, who would later win his first Grand Slam that year. He took the first set 6–0 before losing in three sets. World Tennis reported that "The newspapers and magazines in Puerto Rico have put Khrushchev (Soviet leader behind the
Cuban Missile Crisis) on the second page and Charlito on the first". He attended and graduated from the
University of California, Los Angeles, where he won the
NCAA men's singles and doubles with
Ian Crookenden of New Zealand in 1966, one year after his friend and teammate
Arthur Ashe won those titles. He reached No. 1 in the U.S. rankings in 1967 and became the first man in over 30 years to win the U.S. National Indoors in successive years. This tournament was the biggest indoor tournament in the world. While at UCLA, he received coaching from
Pancho Segura at the Beverly Hills Tennis Club. Pasarell competed in major tournaments from 1960 through 1979, with his most successful showings coming in doubles. He reached the finals in men's doubles at the U.S. Championships in 1965 with Frank Froehling and 1969 with Dennis Ralston, the
French Open with Arthur Ashe in 1970, and the
Australian Open in 1977 with
Erik van Dillen. He was a quarterfinalist at the
U.S. National Championships in 1965 and
Wimbledon in 1976. Pasarell was also a member of the U.S.
Davis Cup team in 1966, 1967, 1968, and 1974. In doubles, Pasarell's most significant wins were the 1967
U.S. National Indoor Championships with Arthur Ashe; the inaugural American Airlines Games in 1974 with Sherwood Stewart which evolved to the current tournament in Indian Wells and the Alan King Classic in 1976 with Arthur Ashe. The latter two at the time were two of the richest most prestigious tournaments in the world. In 1969, Pasarell played
Pancho Gonzales in what was, until 2010, the
longest match in Wimbledon history in terms of the number of games played. The 41-year-old Gonzales finally defeated the 25-year-old 22–24, 1–6, 16–14, 6–3, 11–9 after a battle that lasted 5 hours and 12 minutes.{{cite news |url=https://news.bbc.co.uk/sport2/hi/tennis/wimbledon_history/3751227.stm 1977 was Pasarell's last full-time tour and he started the year very well with a last 16 appearance in the Australian Open losing to eventual runner up
Guillermo Vilas. A semifinal at the South Australian Open including a win over Arthur Ashe (in their last match) and a quarterfinal at the American Airlines Games (a forerunner of the Indian Wells event) with wins over
Balázs Taróczy,
Vijay Amritraj and
Roscoe Tanner before losing narrowly to then world No. 4
Brian Gottfried in three sets. He then had a bad run of form signalling the slow down of his career. He finished ranked 77 on the ATP computer and 25 in the U.S. He had also started the year well in doubles with Erik van Dillen. In 1978, Pasarell's career continued to wind down, he was not given a wild card to Wimbledon and lost in the first round of qualifying to
Jan Šimbera. In 1979, he qualified for both Wimbledon and the US Open and started to play veterans events. He made his last attempt to qualify for the main draw at Wimbledon in 1984 aged 40 when he was not invited to take part in the over 35's singles event and lost in the first round to
Jeff Turpin. He continued to play regularly on the seniors' tour until the end of 1985 and then stopped playing completely in 1988. He returned in 1992 to play regularly in the US Open Seniors events until his last appearance in 2002, he also played in a veterans event in Puerto Rico in 1993.
Long matches Pasarell's match with Gonzales was the longest at Wimbledon until beaten in 2010 by the match between
John Isner and
Nicolas Mahut which lasted 11 hours and 5 minutes over three days and comprised 183 games. However, in 1968 on February 17,
Allison Danzig of
The New York Times reported that Pasarell played 9 hours and 12 minutes of tennis in the U.S. National Indoors in just over 24 hours. He played a 6-hour 20 minute doubles with
Ron Holmberg losing to
Mark Cox and
Bobby Wilson 26–24, 17–19, 30–28. Then less than 15 hours later the reigning two time champion lost in front of a capacity crowd to
Clark Graebner in a semifinal that lasted 3 hours 12 minutes the score being 16–14, 4–6, 8–6, 4–6, 6–3. Danzig wrote: "In all, Pasarell played 217 games in just over 24 hours, and that must stand as a record in a National Championship tournament". These matches were played when the game was slower and also no seats were allowed on the court. ==Playing style==