I don't want to hear from anyone who didn't say before the 5th started that Houck should come out for the 5th. I am the only one who said it, and I think there was a valid reason for not sending Houck out for the 3d time through the Yankees order.
As for sample size, Houck doesn't have a big one, so Cora has to go with what he's got. As someone else has already pointed out, Houck stinks in the 4th and 5th innings.
Plus Whitlock has been the Sox best reliever (WAR-wise) on the Sox, at least, before this game, and Whitlock can go 2 innings easily.
Hindsight says shoulda,woulda, coulda gone with Houck, but foresight said, even when he is pitching great guns, Houck comes apart 3d time through the order--or the 5th inning, take your pick.