After playing in the 1962 Interzonal in Stockholm, Petrosian qualified for the Candidates Tournament in Curaçao along with Pal Benko, Miroslav Filip, Bobby Fischer, Efim Geller, Paul Keres, Viktor Korchnoi, and Mikhail Tal. Petrosian, representing the Soviet Union, won the tournament with a final score of 17½ points, followed by fellow Soviets Geller and Keres each with 17 points and the American Fischer with 14. Fischer later accused the Soviet players of arranging draws and having "ganged up" on him to prevent him from winning the tournament. As evidence for this claim, he noted that all 12 games played between Petrosian, Geller, and Keres were draws. Statisticians pointed out that when playing against each other, these Soviet competitors averaged 19 moves per game, as opposed to 39.5 moves when playing against other competitors. Although responses to Fischer's allegations were mixed, FIDE later adjusted the rules and format to try to prevent future collusion in the Candidates matches.
Petrosian was a conservative, cautious, and highly defensive chess player who was strongly influenced by Aron Nimzowitsch's idea of prophylaxis. He made more effort to prevent his opponent's offensive capabilities than he did to make use of his own. He very rarely went on the offensive unless he felt his position was completely secure. He usually won by playing consistently until his aggressive opponent made a mistake, securing the win by capitalizing upon this mistake without revealing any weaknesses of his own. This style of play often led to draws, especially against other players who preferred to counterattack. Nonetheless, his patience and mastery of defence made him extremely difficult to beat. He was undefeated at the 1952 and 1955 Interzonals, and in 1962 he did not lose a single tournament game. Petrosian's consistent ability to avoid defeat earned him the nickname "Iron Tigran". He was considered to be the hardest player to beat in the history of chess by the authors of a 2004 book.