Back to Petrosian and Larsen.
After playing over Larsen's fine victories over Petrosian in Santa Monica (which I will discuss below), a few questions occurred to me:
1. Had any other sitting world champion ever lost two games to the same opponent in a tournament?
2. Had Petrosian, who was so notoriously difficult to defeat, on any other occasion lost two games to the same opponent in a tournament?
3. What was Larsen's lifetime score against Petrosian? Did he always displace such dominance?
1. I found the answer to the first question quickly enough, having a vague memory that Alekhine had lost twice to somebody in AVRO 1938. Sure enough, Fine won both of his games against Alekhine there. Are there any other examples?
2. It also turned out that Larsen was not the only person to win two games against Petrosian in a single tournament. Taimanov had done it in the 1953 Candidates' Tournament, as had Olafsson in the 1959 Candidates' Tournament.
3. Finally, looking up the lifetime score between Petrosian and Larsen revealed an extraordinarily interesting and combative series of contests. Petrosian won the series, +9, -4, =9. These were hard-fought games. They did not draw a game until their tenth encounter. Only 4 of their first 17 games were draws.
To provide some perspective: in the period between 1958 and 1979, when they played those 13 decisive games out of 17 (only 24% draws), Larsen overall had 30% draws and Petrosian had 56% draws.