A Serena Williams-Li Na semifinal will be a mental test for both

Wednesday September 4th, 2013
Li Na fell in straight sets to Serena Williams earlier this year at the West and Southern Open in Cincinnati.
Matthew Stockman/Getty Images

Throughout this U.S. Open Williams has remained poised and focused, staring down opponents as if she were a world-class heavyweight champ looking to defend her title. Come to think of it, that's exactly what she is.

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