Tokyo stocks opened sharply lower Monday, as selling was spurred by fears of global economic instability from an escalating conflict in the Middle East as well as Wall Street weakness late last week. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 647.28 points, or 1.64 percent, from Friday to 38,876.27. The broader Topix index was down 39.20 points, or 1.42 percent, at 2,720.44. On the top-tier Prime Market, decliners were led by securities house, consumer credit, and transportation equipment shares. At 9 a.m., the U.S. dollar fetched 153.29-32 yen compared with 15…