It may be difficult, after just three games, to declare Ryan Zimmerman back to being himself. But following his performance last night, it is also difficult to draw any other conclusion. Since Zimmerman received a cortisone shot about an hour before first pitch Sunday, he has ditched an epic slump and, as if flipping a switch, turned back into the hitter the Nationals expected to bat third for them this season. Last night, Zimmerman went 3 for 4 with a double and a home run, his first homer in 70 at-bats. He can hit the ball with authority, especially to left field, which had been missing all June as his aching right shoulder limited his preparation and stole his strength. Entering Sunday, Zimmerman was 5 for his last 48, a bleak stretch that convinced him to try the cortisone shot. So far, despite any risk to the long-term fitness of his shoulder, it has worked.