Fantastic performance by Isner, was the (far) better player ever since the moment Fed was so kind to hand him over the break in the 2nd set (yes, that was handed over, nothing less). Kept playing better-and-better, and during the final games, Fed had nothing to hit him with anymore, not even close. That final game was telling: three sizzling return winners to settle the deal. Nothing Fed could have done against those, and to me it looked like he'd already given up the match at that point. Everything worked for Isner today, a great victory and fully deserved. Kudos to the US team!
As for a remark, there's by now a disturbing pattern emerging from Fed's best-of-five performances: most usually wins the first set (or even two), but doesn't seem to be able to keep up his level of playing for a longer period anymore.
Looks like a glaring sign of genuine decline to me, and if this pattern doesn't convince folks of this fact, nothing will, I suppose.