Dufner and Khan surge to top of the Doha leaderboard
Dufner, on a two-week trip to the Middle East and ninth in Abu Dhabi last Sunday, was only joint 42nd at halfway, but went to the turn in 32 and then started the back nine with two more birdies.
Former PGA Championship winner Khan then made it a six-way tie when he birdied five of the first six holes to reach nine under par as well.
That was a massive turnaround from last week for the 40-year-old from Essex, who missed the cut by five strokes in the first leg of the European Tour's three-week 'Desert Swing'.
Dufner bogeyed the short 13th, but Khan's sixth birdie came at the 391-yard seventh and with two pars to follow he was out in a six under 30.
South African Branden Grace also birdied three of his first four holes to join the group one behind on nine under.
Khan grabbed his eighth birdie at the 203-yard 13th, but was joined on 12 under when compatriot Chris Wood had five birdies in the first eight.
They were a stroke ahead of Garcia, who opened with a five-foot putt and after missing chances on the following two greens sank a 22-footer at the fourth.
World number four Justin Rose, meanwhile, had parred every hole on the outward half and so was seven adrift.