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It wasn’t enough to swing the first set the other way, but, in hindsight, this point proved a sign of things to come for Rafa Nadal in his US Open semifinal against Juan Martin del Potro.

Nadal ended a long, grueling, criss-crossing exchange by chasing down an excellent Del Potro drop shot and sending it back with an even better one.

Del Potro would hold to win the set in the following game, but that moment seemed to energize Nadal, who wound up running off nine straight games to take the second and, eventually, third sets.