Casey missed 4-foot birdie chances on the last two holes.
They felt like two bogeys, Casey said. They were beyond my control. On 18, I tried to hit it firm in the middle. And it was heading firmly in the middle.
Casey had a 13-under 203 total.
Denmarks Soren Kjeldsen (68) holed a 25-foot putt from across the green at the last to move into second place, while Northern Ireland prodigy Rory McIlroy had the best round of the week, a 7-under 65, to move into third at 9 under.
I had a really good session on the range, then every shot I hit was the shot that Id seen, McIlroy said. I was able to see fades and draws and hit them where I wanted to. It was nice to be able to do that again.
Casey, who has already won in Abu Dhabi and Houston this year to climb to No. 7 in the world ranking, watched the tournament when he was a boy and won the 2006 World Match Play at Wentworth.
The great players have their names etched on this trophy, Casey said. For me it would be nice to get my name on that Roll of Honor. For me, thats the biggest thing.
His 67 was more consistent than his 67 Friday, which included two eagles and three bogeys.
This was more satisfying because there were no dropped shots although yesterday had the fireworks, Casey said. Ive battled the swing a little bit and I hit a couple of poor shots. I wont say Ive got total control of the golf ball right now.
Ross Fisher (67) and Charl Schwartzel (68) were 8 under.
Three-time winner Colin Montgomerie birdied five of the first 12 holes, but bogeyed 13, 15 and 16 and settled for a 69. He was 5 under.
That was not decent at all, really, Montgomerie said. I was very disappointed to bogey 13, I missed a short putt for birdie on 14 and bogeyed the next two. So it was like four bogeys in a row. Then I made a mess of the last. I had a good chance to get into real contention, but not now. To throw it away is very disappointing.
Ernie Els was even par after a 70, and John Daly was 5 over after a 77.