MAR DEL PLATA, Argentina—Feliciano Lopez upset Juan Martin del Potro 4-6, 7-6 (2), 7-6 (4), 6-3 Friday, allowing Spain to escape the first day of the Davis Cup final tied 1-1 tie with Argentina.

David Nalbandian brushed aside David Ferrer 6-3, 6-2, 6-3 in the opening singles, and del Potro was expected to comfortably handle Lopez on his favored hard court.

But Lopez took the two tiebreakers, and del Potro injured his right thigh in the sixth game of the fourth set. After treatment, he lost his serve and Lopez cruised to victory in 3 hours, 19 minutes, hushing the boiste...

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