FLUSHING MEADOWS, N.Y. — It was yet another measure of the instability in women’s tennis that French Open champion Li Na imploded in the first round of the U.S. Open Tuesday, following the reigning women’s Wimbledon champion out the door without winning a set. The sixth-seeded Li sprayed the court with 54 unforced errors to essentially hand Romanian teen Simona Halep the 6-2, 7-5 victory.