Ilie Theodoriu Năstase (Romanian: [iˈli.e nəsˈtase] ; born 19 July 1946) is a Romanian former professional tennis player. He was ranked as the inaugural world No. 1 in men's singles by the Association of Tennis Professionals (ATP) for 40 weeks. Năstase is one of ten players to have won over 100 total ATP-level titles, with 64 in singles and 45 in doubles, among which seven majors: two in singles, three in men's doubles and two in mixed doubles. He also won four Masters Grand Prix year-end championships. He was the first professional sports figure to sign an endorsement contract with Nike, doing so in 1972. Năstase also wrote several novels in French in the 1980s, and was inducted into the International Tennis Hall of Fame in 1991.
At the beginning of his career in 1966, Năstase traveled around the world competing with Ion Țiriac. They represented Romania in the Davis Cup competition, being runners up in 1969, 1971, and 1972. In singles, Năstase won his first tournament at Cannes on 16 April 1967. His first victories against top players happened in 1969 in Stockholm, where he defeated Tony Roche and Stan Smith. Năstase became one of the best players in 1970, with many experts ranking him as the sixth-best player in the world at that time, behind the Australians Rod Laver, Ken Rosewall, John Newcombe, and Tony Roche and the American Arthur Ashe. Năstase's high ranking resulted from his success at the Italian Open in Rome and at the U.S. Indoor Open in Salisbury, Maryland. With Tiriac, Năstase won the men's doubles title at the French Open. In 1971, Năstase was the runner-up at the French Open, where he lost the final in four sets to Jan Kodeš. In December, Năstase won his first Masters Grand Prix title, finishing in front of Stan Smith in a round robin competition.
In 1972, at Wimbledon, Năstase narrowly lost to Stan Smith in an epic five-set final, one of the more exciting championship matches. He won the US Open in a five-set final over Ashe, despite trailing 2 sets to 1 and 4-2 in the fourth set. This tournament was the only event of the year in which all the best players participated. In the Davis Cup, Năstase was undefeated in singles until losing to Stan Smith in the final played on clay in his native Bucharest. In December at the year-end tour finals, Năstase defeated Smith, winning his second consecutive Masters Grand Prix title.
In 1973, Năstase won 17 tournaments, including the French Open where he beat 33-year-old Nikola Pilić in the final in straight sets. "Throughout the match it was Nastase's backhand that won the points". He also won a doubles title at Wimbledon, and a third Masters title. He was the world No. 1 in the ATP rankings that year. He also won the 'Martini and Rossi' Award, voted for by a panel of journalists and was ranked No. 1 by an international poll of 17 tennis writers, Tennis Magazine (U.S.), Bud Collins, Rino Tommasi and Rex Bellamy. In the Davis Cup, he won seven of eight singles rubbers. In matches against the other top players, Năstase was 1–0 against Newcombe and 1–1 against Smith. The Romanian won the French Open without dropping a set (a feat repeated by Björn Borg in 1978 and 1980 and by Rafael Nadal in 2008, 2010, 2017 and 2020), and he won the French Open (clay), Rome (clay) and Queen's Club (grass) in succession. Năstase was seeded No. 2 for Wimbledon, behind the defending champion Stan Smith. When the newly formed ATP withdrew its players from the tournament following the suspension by the ITF of Yugoslav Nikola Pilić, only three ATP players (Năstase, Roger Taylor and Ray Keldie) defied the boycott and were fined by the ATP's disciplinary committee. Năstase was promoted to No. 1 seed for the players in the subsequently weakened field and publicly stated his support for the ATP action but insisted that as a serving captain, he was under orders from the Romanian army and government to compete and thus could not boycott the tournament. Some contemporary press speculation, and later biographies have suggested Năstase contrived to lose his fourth-round match to American Sandy Mayer, but to have lost any earlier to a considerably less able player would have been too obvious. Năstase never has commented publicly on this speculation.
In 1974, he was the only player to qualify for both the WCT Finals and the Masters Grand Prix finals. Năstase played well in the Masters, in particular against Newcombe in the semifinals. (Năstase finished his career with a 4–1 record versus Newcombe, losing only their first match in 1969.) The Romanian, however, lost the final to Guillermo Vilas in five sets.
For the fifth consecutive year, Năstase reached the Masters Grand Prix final in 1975, where he defeated Björn Borg in three straight sets.
During the first half of 1976, Năstase won four tournaments (Atlanta WCT, Avis Challenge Cup WCT, US Open Indoor, and La Costa), and head-to-head, he led Connors 2–1, Vilas 1–0, Ashe 1–0, and Borg 2–0. Năstase did not enter the Australian Open, which was again avoided by most of the top players. Năstase was prevented from entering the French Open because he participated in World Team Tennis. In the second half of the year, third-seeded Năstase lost in straight sets to Borg in the men's singles final of Wimbledon and in the semifinals of the US Open. Năstase won three other tournaments during the second half of the year, the Pepsi Grand Slam, South Orange, and the four-man tournament of Caracas, Venezuela, in October (not to be confused with the Caracas WCT tournament in March), making seven tournament championships for the year. Năstase was the world No. 3, behind Connors and Borg.
In 1977, Năstase finished No. 9 in the ATP rankings. He was a quarterfinalist at the French Open and at Wimbledon (losing to Borg), and participated in the WCT Finals. During his quarterfinal match at Wimbledon Năstase had a row with umpire Jeremy Shales. Shales called him "Năstase" when asking him to move to the advantage court, "like a master speaks to a naughty schoolboy." (Năstase has also said Shales asked him to pick up a piece of paper that had blown onto the court, saying, "Năstase, pick up that paper.") Năstase angrily replied "You call me Mr. Năstase!". Mr. Nastase later became the title of his autobiography.
He was still one of the 20 best players in 1978; at Wimbledon, he again reached the quarterfinals.
Năstase retired from the tour in October 1985 at the age of 39 after playing in the Grand Prix de Tennis de Toulouse, but he did play the challenger tournament at Dijon in June 1988.
Năstase earned the nickname "Nasty" early in his career, after routinely acting in an inappropriate manner on court, making himself disliked by competitors and fans alike. He would at times avoid the lockerroom after tennis matches, scared of direct confrontation with players he had antagonized on the court.
In the second round of the 1976 US Open against Hans-Jürgen Pohmann, there were several controversial moments involving Năstase. At 5–5 in the third and final set Năstase was furious at a photographer and hit a ball at him and swung his racket near him. The crowd were at fever pitch by this point. Then Pohmann began cramping badly in his leg. With the aid of the tournament physician, who attended the leg, Pohmann saved three match points and the set entered a final set tie-break. Năstase was screaming at the umpire and directing obscenities at the crowd. Pohmann had two match points but Năstase won and then screamed at Pohmann as the two approached the net. The umpire refused to shake Năstase's hand as Ilie continued raving. Many thought Năstase should have been disqualified. Later, Năstase claimed the match should have been forfeited to him when Pohmann was unable to continue play immediately (he and Pohmann had to be separated in the clubhouse after the match).
In October 1977 at the Raquette d'Or tournament, Năstase used a 'spaghetti string' (double-strung) racket to end Guillermo Vilas's 46-match winning streak. The racket was known for creating large amounts of top spin and unpredictable bounces. Vilas quit the match in protest at the use of the racket. A few days later, the ATP banned the use of such racquets.