When rain brought a premature end to the match, the Cobras had reached 172 for seven wickets in pursuit of a target of 206 in 48 overs. With 8.1 overs remaining in their innings, the Cobras' required Duckworth Lewis par score was 169.
Duminy displayed his maturity as the Warriors made a sterling effort in defending their modest total. He faced 68 balls and struck three fours.
Importantly, he remained calm with wickets falling around him as the Warriors spinners, led by Johan Botha and Nicky Boje (three for 26), turned the screws on the visitors.
The most decisive blow of the night, however, was the four Rory Kleinveldt hammered off Wayne Parnell before the players scampered off the field for the final time under a heavy downpour. Had it not been for that boundary, the Warriors and not the Cobraswould have claimed top spot on the log.
Earlier, Cape Cobras seamer Charl Langeveldt ripped the heart out of the Warriors' middle-order to help restrict the homeside to 201 for nine. That total was adjusted to 205 after rain brought a brief halt to proceedings with nine balls remaining in Warriors' innings.
Langeveldt, who had been a touch expensive in his first spell, came back strongly to claim the wickets of Colin Ingram (23), Justin Kreusch (26), Johan Botha (11) and Athi Dyili (4) to finish the innings with figures of four for 46.
The Warriors won the toss under gloomy skies and elected bat in the top-of-the-table clash.
Jon-Jon Smuts (49) and Nicky Boje (27) got the Warriors off to a decent enough start, posting 62 runs for the first wicket in 14 overs. But the introduction of spinners Robin Peterson and JP Duminy put the skids on their pursuit of any total of substance. And as pressure built on a St George's pitch which proved to be typically low and slow, the Warriors failed to establish any further meaningful partnerships.
Duminy struck early claiming the scalps of opener Nicky Boje and Arno Jacobs to finish with two for 38.
Peterson was superb conceding only 22 runs in 9.3 overs while picking up the wickets of Craig Thyssen Wayne Parnell.
Kleinveldt was also miserly until Rusty Theron hit him for six and four off consecutive deliveries. He still managed to finish with the impressive analysis of one for 38 in 10 overs.