If it has two power connectors on the card, yes, it requires that both of them be filled. You can just use a molex to 6 pin PCIe adapter if you don't have the second one on your PSU.
That said, it would be extremely unusual for a 1000W PSU to only have a single PCIe connector. The only reason to get such a high wattage is to run multiple video cards. What PSU do you have?