I took this week’s puzzle from Scottish chess historian Douglas Griffin’s Twitter feed. If Twitter is still alive by the time you read this it’s well worth following.

In the first round of the 1978 Olympiad Wales had to face the mighty Soviet Union. On top board, John Cooper was pitted against former World Champion Tigran Petrosian, perhaps the most difficult player of his generation to beat.

Petrosian was also famous for his exchange sacrifices, and in this position he’d just played 36… Rxf4, capturing a Welsh bishop.

Cooper made the obvious recapture, went wrong a few moves later and soon lost. But he’d missed the chance for a major upset.

If he’d looked beyond the obvious (I’d imagine he was in time trouble) he’d have seen the forced mate: 37. Rb7+! Kd8 38. Ra1 Kc8 39. Rab1 f2+ 40. Kf1 Kd8 41. Ra7! Kc8 42. Ra8+ Kc7 43. Rab8 Rxh6 44. R1b7#.

Congratulations to everyone who spotted this. I note that Anurag and Paul, amongst others, on our WhatsApp group, had seen the right idea: well done!

I think Petrosian’s 36… Rxf4 deserves ?! rather than ? as he was in trouble anyway, so it was certainly worth a punt. His real mistake was 34… Rxe4? (Rb8!). Interesting game, anyway and well worth your time looking at it.

Here’s the complete game. Click on any move for a pop-up window.