NEW YORK, Jan 5 - U.S. blue chips opened slightly higher on Wednesday, but tech stocks were weaker, hurt by microchip maker Xilinx Inc. lowering its revenue guidance, while investors remained concerned about rising interest rates. The Dow Jones industrial average was up 18.48 points, or 0.17 percent, at 10,649.26. The Standard & Poor's 500 Index was up 1.73 points, or 0.15 percent, at 1,189.78. The Nasdaq Composite Index was down 0.17 of a point, or 0.01 percent, at 2,107.69.