Nvidia Corp NVDA.O, Qualcomm Inc QCOM.O, Advanced Micro Devices Inc AMD.O and Intel Corp INTC.O were down between 0.7% and 1.8%. By Shubham Batra and Ankika Biswas Dec 22 (Reuters) - Wall Street's main indexes were set to open lower on Thursday as fresh data underscored strength in the U.S. economy and aggravated concerns over the Federal Reserve's continued policy tightening. Wall Street's main indexes marked their biggest daily gain so far in December on Wednesday, with help from upbeat Nike Inc NKE.N and FedEx Corp FDX.N quarterly earnings, as well as improving consumer confidence and easing inflation expectations.