 USA: Tampa - Singles - Main |
|---|
| 1/16-finals | Reneberg R. | Duncan L. | 2:0 (7:63, 6:2) | details | 29.04.1991 |
 Brazil: Guaruja - Singles - Main |
|---|
| 1/16-finals | Wostenholme M. | Duncan L. | 2:0 (7:63, 6:1) | details | 04.02.1991 |
 Greece: Athens - Singles - Main |
|---|
| 1/8-finals | Sanchez J. | Duncan L. | 2:0 (6:4, 6:0) | details | 03.10.1990 |
| 1/16-finals | Altur J. F. | Duncan L. | 0:2 (3:6, 6:7) | details | 01.10.1990 |
 Italy: Palermo - Singles - Main |
|---|
| 1/16-finals | Carbonell T. | Duncan L. | 2:0 (6:3, 6:2) | details | 24.09.1990 |
 France: Bordeaux - Singles - Main |
|---|
| Quarter-finals | Forget G. | Duncan L. | 2:1 (6:1, 6:7, 6:0) | details | 14.09.1990 |
| 1/8-finals | Duncan L. | Ingaramo M. | 2:0 (6:3, 6:2) | details | 12.09.1990 |
| 1/16-finals | Duncan L. | Pioline C. | 1:0 RET. (6:3, 3:2) | details | 10.09.1990 |
| USA: US Open - Singles - Main |
|---|
| 1/64-finals | Grabb J. | Duncan L. | 3:0 (6:4, 6:2, 6:4) | details | 27.08.1990 |
 Czech Republic: Prague - Singles - Main |
|---|
| 1/16-finals | Duncan L. | Skoff H. | 0:2 (2:6, 1:6) | details | 06.08.1990 |
 United Kingdom: Wimbledon - Singles - Main |
|---|
| 1/64-finals | Broad N. | Duncan L. | 3:0 (6:4, 6:2, 7:6) | details | 30.06.1990 |
| Italy: Bologna - Singles - Main |
|---|
| Quarter-finals | Duncan L. | Rosset M. | 0:2 (2:6, 3:6) | details | 22.06.1990 |
| 1/8-finals | Cane P. | Duncan L. | 0:2 (5:7, 3:6) | details | 20.06.1990 |
| 1/16-finals | Altur J. F. | Duncan L. | 0:2 (3:6, 0:6) | details | 18.06.1990 |
| Italy: Florence - Singles - Main |
|---|
| Final | Larsson M. | Duncan L. | 2:1 (6:7, 7:5, 6:0) | details | 17.06.1990 |
| Semi-finals | Duncan L. | Camporese O. | 2:0 (6:2, 6:3) | details | 16.06.1990 |
| Quarter-finals | Carbonell T. | Duncan L. | 0:2 (5:7, 3:6) | details | 15.06.1990 |
| 1/8-finals | Perez D. | Duncan L. | 0:2 (3:6, 1:6) | details | 13.06.1990 |
| 1/16-finals | Duncan L. | Davin F. | 2:1 (2:6, 7:6, 6:2) | details | 11.06.1990 |
| France: French Open - Singles - Main |
|---|
| 1/64-finals | Azar R. | Duncan L. | 3:0 (6:3, 6:1, 6:1) | details | 28.05.1990 |
| Italy: Rome - Singles - Main |
|---|
| 1/32-finals | Pescosolido S. | Duncan L. | 2:0 (6:2, 6:3) | details | 14.05.1990 |
| USA: Kiawah Island - Singles - Main |
|---|
| 1/16-finals | Tarango J. | Duncan L. | 2:0 (6:3, 6:4) | details | 07.05.1990 |
 Spain: Barcelona - Singles - Main |
|---|
| 1/32-finals | Duncan L. | Azar R. | 0:2 (2:6, 4:6) | details | 09.04.1990 |
| USA: Miami - Singles - Main |
|---|
| 1/32-finals | Duncan L. | Sanchez E. | 0:2 (4:6, 1:6) | details | 18.03.1990 |
| 1/64-finals | Cancellotti F. | Duncan L. | 0:2 (1:6, 6:7) | details | 16.03.1990 |
| USA: Indian Wells - Singles - Main |
|---|
| 1/32-finals | Dyke B. | Duncan L. | 2:1 (4:6, 6:1, 6:2) | details | 05.03.1990 |
| USA: Memphis - Singles - Main |
|---|
| 1/16-finals | Duncan L. | Curren K. | 0:2 (4:6, 2:6) | details | 28.02.1990 |
| 1/32-finals | Evans K. | Duncan L. | 0:2 (4:6, 2:6) | details | 26.02.1990 |
| USA: Philadelphia - Singles - Main |
|---|
| 1/32-finals | Korda P. | Duncan L. | 2:0 (6:3, 6:1) | details | 19.02.1990 |
 Canada: Toronto 2 - Singles - Main |
|---|
| 1/32-finals | Nijssen T. | Duncan L. | 2:0 (6:3, 6:3) | details | 12.02.1990 |
| USA: San Francisco - Singles - Main |
|---|
| 1/8-finals | Rive J. | Duncan L. | 2:1 (4:6, 6:3, 6:3) | details | 07.02.1990 |
| 1/16-finals | Duncan L. | Evernden K. | 2:1 (7:5, 5:7, 7:5) | details | 05.02.1990 |
