20 - Consecutive games Washington has played against Pittsburgh without a win in which they scored fewer than three goals (the last one of those was a 1-0 win on January 11, 2012). Here, via Hockey-Reference, is a quick look at those games:
Granted, a few of those games could've been won with fewer than three goals (and one of them would've been, if not for a late empty netter). But, unsurprisingly, three goals has been a pretty important benchmark for the Caps in their Ovechkin Era battles with the Pens - they've gone 2-15-2 when failing to score three times, and 21-7-6 when reaching that mark (including 20-4-4 in the last 28).
On a related note, after going 45-2-2 during the regular season in games in which they allowed fewer than two goals, the Caps are now 4-3 in such games in this postseason.