Tennis ace Leander Paes has pulled out of the US Open mixed doubles semifinals due to back spasms. This came as a massive blow to India's chances in the Davis Cup. The tie against Japan is scheduled from September 16 to 18 in the Japanese capital of Tokyo.Paes and his Russian partner Elena Vesnina, seeded seventh, gave a walkover to unseeded Americans Melanie Oudin and Jack Sock. Paes and Bhupathi have already been knocked out of the men's doubles quarterfinal after losing to Poland's Mariusz Fyrstenberg and Marcin Matkowski in straight sets.The sixth seeded Polish duo won 6-4 7-6 (7-4) in an hour and 43 minutes against the fourth seeded Indian pair.