They were yet to tee off, but had been joined on nine under par by US Ryder Cup star Jason Dufner.
The American had six birdies in his first 12 holes, while Swede Peter Hanson - the man Dufner beat in the Ryder Cup singles at Medinah Country Club - was four under for the day through 14 and up to seven under for the week at Doha Golf Club.
Dufner bogeyed the short 13th, but South African Branden Grace birdied three of his first four holes to replace him in 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.