Why did Petrosian stop playing the Petroff

At the halfway mark in the 1969 World Championship between Petrosian and Spassky, the match score was level. Petrosian only needed to draw the match to retain his title, and with his super-solid Petroff it looked like he was going to wrap things up. But in game 17 and 19 Petrosian suddenly switched to Sicilian, losing calamitously. John Saunders retraces the course of the match that decided who would defend the title against Fischer three years later.

Cheating controversy at Pro Chess League

Tigran Petrosyan's response to Wesley So's accusations. : r/chess

The American Grandmaster Who Could Become World Champion

MIME Attachment View

The petroff -_an_expert_repertoire_for_black_-_sakaev

Petrov Defense: Opening Guide for White & Black - Chessable Blog

Middlegame Archives - British Chess News

If Petrosian Sacrifices A Piece, Resign

Mikhail Tal Defeats Tigran Petrosian In 23 Moves - Tal vs

Why did Petrosian stop playing the Petroff

Petrov Defense: Opening Guide for White & Black - Chessable Blog

Winning With the Petroff (Batsford Chess book by Anatoly Karpov

Since we are talking about Tigran Petrosian once again, I decided

Evidence in favor of Tigran Petrosian NOT cheating -- When asked