New Era for Tennis will begin once a YOUNG BLOOD comes in and wins a slam, and stays on top. That could've happened in 1009 when DelPo won the USO but he got injured and hasn't returned on that level.
Negative. Even if Del Potro had remained healthy, a new era wouldn't have started. One player doesn't make a new era, it takes a whole generation of players stepping up - either that or a single player taking over Federer style and winning everything under the sun, which is quite unlikely.