Playing Hastings for the first time in 1950/51, he beat the French champion Nicolas Rossolimo and at Southsea in 1950, defeated both Efim Bogoljubov and Savielly Tartakower.

In 1952/1953 he shared the first place at Hastings with Harry Golombek, Antonio Medina García and Daniel Yanofsky.

On both of these occasions, he won an individual silver medal on first board; in 1968, his score was bettered only by the World Champion, Tigran Petrosian.

At the Leipzig 1960 Olympiad, he defeated then-World Champion Mikhail Tal with the white pieces in a Modern Benoni:1.d4 Nf6 2.c4 e6 3.Nc3 c5 4.d5 exd5 5.cxd5 d6 6.e4 g6 7.Bd3 Bg7 8.Nge2 O-O 9.O-O a6 10.a4 Qc7 11.h3 Nbd7 12.f4 Re8 13.Ng3 c4 14.Bc2 Nc5 15.Qf3 Nfd7 16.Be3 b5 17.axb5 Rb8 18.Qf2 axb5 19.e5 dxe5 20.f5 Bb7 21.Rad1 Ba8 22.Nce4 Na4 23.Bxa4 bxa4 24.fxg6 fxg6 25.Qf7+ Kh8 26.Nc5 Qa7 27.Qxd7 Qxd7 28.Nxd7 Rxb2 29.Nb6 Rb3 30.Nxc4 Rd8 31.d6 Rc3 32.Rc1 Rxc1 33.Rxc1 Bd5 34.Nb6 Bb3 35.Ne4 h6 36.d7 Bf8 37.Rc8 Be7 38.Bc5 Bh4 39.g3 1–0.

[3]This victory made Penrose the first British player to beat a reigning world champion since Joseph Henry Blackburne defeated Emanuel Lasker in 1899.