Day recovered from an early bogey with four birdies and one solitary bogey at the 13th to be at least within striking distance of Dufner who has found form after nearly twelve months without a top ten.
Dufner leads by one over Joel Dahmen and Max Homa with two-time winner of this event, Rory McIlroy, and Patrick Reed another four shots back and tied for 4th place.
Dufner is playing this event for just the second occasion in the past nine years but his round of 63 on day two suggests the game that has seen him win five events on the PGA Tour including the 2013 PGA Championship is returning.
With the lack of recent experience in contention from the leader however and the two non-PGA Tour winners one behind the door is open over the final 36 holes for many others including Day to work their way into the mix for the title.
Matt Jones is in 21st place at 2 under and three behind Day while John Senden is another shot back in 28th place.
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