Boris Spassky - Wikipedia

Spassky's Pawn Game: Larsen vs Spassky, Belgrade 1970 – Chess Universe

Why did Petrosian stop playing the Petroff

Petrosian vs Spassky, World Championship match 1966, Queen Sac

BORIS SPASSKY VS TIGRAN PETROSIAN WORLD CHAMPIONSHIP MATCH 1966..TORRE ATTACK:CLASSICAL DEFENCE, DAILY CHESS:A very interesting,baffling and ultimately instructive game.., By Chess Hustlers

Petrosian v Spassky: The World Championships 1966 and 1969 (Paperback)

Petrosian vs. Spassky World Championship 1966 - GM Ben Finegold

Tigran Petrosian Top Chess Players

Tigran Petrosian photos

The Fischer-Petrosian Candidates' Final (Buenos Aires, 1971) with annotations by Korchnoi, Furman, Kholmov & Polugaevsky.

Bobby Fischer, Everything Chess Wiki