12‑Jan‑1977 | Birmingham WCT | Carpet | R16 | 23 | 26 | Cliff Drysdale [RSA] d. Okker | 6-1 7-5 | | | | | | | | | |
7‑Jan‑1976 | Columbus WCT | Carpet | QF | 11 | 36 | Cliff Drysdale [RSA] d. (3)Okker | 3-6 7-6(5) 7-6(5) | | | | | | | | | |
24‑Jun‑1974 | Wimbledon | Grass | R32 | 4 | 13 | (7)Okker d. Cliff Drysdale [RSA] | 4-6 6-3 6-3 6-3 | | | | | | | | | |
25‑Mar‑1974 | Rotterdam | Carpet | SF | 3 | 23 | (2)Okker d. (4)Cliff Drysdale [RSA] | 6-3 3-6 6-3 | | | | | | | | | |
3‑Mar‑1974 | Miami WCT | Hard | SF | 3 | 23 | Cliff Drysdale [RSA] d. (2)Okker | 6-0 1-6 7-5 | | | | | | | | | |
11‑Feb‑1974 | Toronto WCT | Carpet | R16 | 4 | 23 | Okker d. Cliff Drysdale [RSA] | 6-3 6-4 | | | | | | | | | |
17‑Sep‑1972 | Montreal WCT | | QF | | | Okker d. Cliff Drysdale [RSA] | 4-6 7-5 6-2 | | | | | | | | | |
29‑Jul‑1972 | Louisville WCT | Clay | QF | | | Cliff Drysdale [RSA] d. Okker | 7-5 7-5 | | | | | | | | | |
8‑Aug‑1971 | Boston WCT | Hard | QF | | | (3)Cliff Drysdale [RSA] d. (5)Okker | 6-4 4-6 6-4 | | | | | | | | | |
24‑Jul‑1971 | Louisville WCT | Clay | F | | | Okker d. Cliff Drysdale [RSA] | 3-6 6-4 6-1 | | | | | | | | | |
7‑Jun‑1971 | Bristol | Grass | QF | | | (4)Cliff Drysdale [RSA] d. (5)Okker | 7-6 6-7 7-6 | | | | | | | | | |
3‑May‑1971 | Rome | Clay | QF | | | (6)Okker d. (3)Cliff Drysdale [RSA] | 6-3 6-4 | | | | | | | | | |
1‑May‑1971 | Dallas WCT | Carpet | QF | | | (6)Okker d. (3)Cliff Drysdale [RSA] | 6-3 6-7 6-3 | | | | | | | | | |
29‑Sep‑1970 | Vancouver | Carpet | QF | | | Okker d. Cliff Drysdale [RSA] | 6-3 6-4 | | | | | | | | | |
19‑Jul‑1970 | Leicester | Grass | SF | | | Okker d. Cliff Drysdale [RSA] | 6-3 8-6 | | | | | | | | | |
4‑Mar‑1970 | Wembley | Carpet | QF | | | Okker d. Cliff Drysdale [RSA] | 6-3 6-2 | | | | | | | | | |
4‑Aug‑1969 | Hamburg | Clay | SF | | | Okker d. Cliff Drysdale [RSA] | 4-6 6-3 3-6 6-4 | | | | | | | | | |
21‑Jul‑1968 | Gstaad | Clay | F | | | Cliff Drysdale [RSA] d. Okker | 6-3 6-3 6-0 | | | | | | | | | |
11‑Jun‑1967 | Bristol | Grass | F | | | Okker d. Cliff Drysdale [RSA] | 6-2 5-7 8-6 | | | | | | | | | |
4‑May‑1967 | Davis Cup EUR R1: NED vs RSA | Clay | RR | | | Okker d. Cliff Drysdale [RSA] | 6-2 6-2 0-6 7-5 | | | | | | | | | |
13‑May‑1966 | Davis Cup EUR QF: NED vs RSA | Clay | RR | | | Cliff Drysdale [RSA] d. Okker | 6-3 6-4 4-6 6-2 | | | | | | | | | |
30‑Apr‑1965 | Davis Cup EUR R1: NED vs RSA | Clay | RR | | | Cliff Drysdale [RSA] d. Okker | 6-2 6-1 6-2 | | | | | | | | | |
4‑Feb‑1964 | Benoni | Hard | R16 | | | Cliff Drysdale [RSA] d. Okker | 6-2 8-6 | | | | | | | | | |