Fresh off a sizzling 61 on Friday, overnight leader Simon Khan managed a 2-under 70 in the third round to finish alone in second place at 16-under-par 200. James Kingston was two shots further back at 14-under-par 202.
Casey got off to a quick start Saturday on a course that has yielded plenty of birdies this week. The Englishman putted from off the green for a birdie at the par-4 first and chipped his third shot within a few inches of the hole for a tap-in birdie at the par-5 second.
At the par-4 fourth, Casey hit his second shot to 4 feet for another birdie before playing a remarkable approach to the fifth. Casey's second shot to the par-5 came to rest 7 feet past the cup and he converted the eagle try to open a two-shot lead over Khan at 17 under.
Casey left his approach just off the green at the par-4 eighth, but again used the putter for another birdie to go out in 30.
The 26-year-old lost some of his momentum on the inward half at the par-3 12th after he could not get up and down from a greenside bunker. The problems continued at the very next hole when he failed to convert a 2-foot putt en route to another bogey.
Casey persisted, however, and drained a long birdie putt at the par-3 14th. He then knocked his approach to 10 feet and ran home the birdie try to increase his advantage over Khan to four strokes.
Casey closed out his round with a two-putt birdie at the last to give himself a cushion heading into the final round.
'I probably would have taken that at the start of the day,' said Casey, who established a new 54-hole tournament record. 'As it panned out I still felt I left a few shots out there. But the game is in good shape and I am looking forward to tomorrow.'
Khan, who joined an elite group with a 27 on the front nine Friday, cooled down during the third round and tallied his first birdie of the day at the fifth.
'You try and forget what you did on the previous day on certain holes, but it is difficult,' said Khan. 'I just said to myself to be patient and that you never know what is going to happen around this course.'
The Englishman stumbled to a bogey at the par-5 11th, but remained in contention thanks to some solid strokes down the stretch.
Khan hit his approach to 3 feet for a birdie at the 17th and landed his second shot on the front edge of the green at the par-5 last. The 31-year-old then took two putts for a birdie to finish three shots off the pace.
John Bickerton fired a 9-under 63 to move into a tie for fourth. Bickerton was joined by Colin Montgomerie and Philip Golding at 12-under-par 204. Nick O'Hern, Peter Lawrie and Alastair Forsyth followed at 11-under-par 205.