Basketbawful theorizes that the problem was Vince Carter:
A line of 31 points and 13 rebounds sounds pretty good, but shooting 12-for-33 (including 1-for-8 from three-point range) sounds decidedly less good. But it wasn't just the poor shooting, it was the kind of shots he was taking. He reverted to his late-Toronto form and started taking the sort of bailout, long-distance shots that make Lawrence Frank want to gouge out his own eyes. Even worse, his errant shot selection prevented the Nets from building any sort of cushion, and thereby allowed the Pacers to steal Game 1. On the upside, Carter did fall on his head, so the afternoon wasn't a complete waste.
Click the link above to see the gory series of "falling on head" photos.