I say it's unsurprising because the pace of the game in the third indicated that would be the end result. The two teams exchanged scoring chances but to the naked eye it didn't seem like either team was on the verge of winning the game at any given second.
The stat sheet tells a very different story. The Capitals outshot the Rangers 13-4 in the final frame, including four shots from Alex Ovechkin. In fact, Ovechkin had one heck of a third period on both ends of the ice, blocking five Rangers shots.
New York hasn't gotten much going on offense (Rick Nash has been completely invisible) so they've had to rely on 26 saves from Henrik Lundqvist to get them to overtime. It might not matter. The Rangers haven't won a regulation playoff game in Washington since Game 2 of the 2009 series.