Khan's countrymen Lee Slattery and Oliver Wilson are one stroke back at minus-6. Alexander Noren, Carlos Rodiles, Zane Scotland, Taichi Teshima, Ricardo Gonzalez and Johan Axgren are another stroke further back at 5-under-par 67.
Khan flew out of the gate with birdies on one and two, both from 20 feet out. He quickly jumped to 4-under thanks to a 30-foot eagle putt on the par-5 third. However, he gave a stroke back with a bogey at four.
The 35-year-old rolled in a birdie putt on the par-4 eighth. He parred the next four around the turn.
Khan converted a birdie putt on the par-4 13th to move to 5 under at Gut Kaden. He took advantage of the par-5s down the stretch with birdies on Nos. 15 and 17.
'I felt really good going out,' said Khan, who did not qualify for last week's British Open. 'I played in the last two (Opens) and felt I was better off doing some practice so I didn't watch a lot of it.'
Khan returned to an old putter and changed his grip while he practiced at home last week.
'I went back to an old putter, changed my grip a little bit to how I used to putt as I did as a kid, with my finger down the shaft,' Khan admitted. 'I noticed (Padraig) Harrington does that although with the other hand. It felt really good last week and the first three holes today I holed three good putts.'
Slattery also had a fast start with a birdie on one and an eagle at the third. He drained birdie efforts on eight and nine to turn in minus-5. Slattery capped a bogey-free round with a birdie on 17.
Wilson started on the back nine and posted four birdies over his first nine holes. He dropped a shot at one, then birdied three more holes on his way in to share second.
'I got off to a nice start by holing a few putts early on,' Wilson said. 'But I felt quite uncomfortable, to be honest, with my swing, but managed to keep putting well. I holed a few surprise putts towards the end, which was nice.'
Niclas Fasth, the 2005 winner, carded a 4-under-par 68 Thursday. He shares 10th place with Robert Rock, Andres Romero, David Frost, Stephen Gallacher, Marcus Higley, Charley Hoffman, Marc Warren, John Bickerton, Michael Campbell, Paul Casey and David Lynn.
Defending champion Robert Karlsson is part of a large group tied for 22nd at minus-3.