Ogilvy, who reached the championship match for the third time in four years, made six birdies and one unlikely par on a sunny morning at Dove Mountain to put himself in solid position for the afternoon.
Casey did not win his first hole until No. 10, when he holed out from 200 yards with a 6-iron. Ogilvy won the next hole after hitting into a cactus, taking a penalty drop into the desert, then holing a 60-foot chip for par as Casey made bogey.
Although the final is 36 holes, no one has come back from more than two holes down to win a match all week. And in the previous 10 finals, the player trailing after the morning round has come back to win only twice - Jeff Maggert, who was 2 down in 1999, and Tiger Woods, who trailed Davis Love III by one hole in 2004.
Casey came into final match having led in 79 of the 80 holes he had played in the five previous 18-hole matches. He had a chance to become the first Match Play champion to never trail the entire week.
But all that changed quickly.
Ogilvy holed a 6-foot birdie putt on the opening hole, and Casey missed from 5 feet to fall behind for the first time this week.
The Englishman was lucky the deficit did not grow even more.
Ogilvy had birdie putts inside 12 feet on the next three holes and missed them all, but he built his lead when Casey three-putted from the fringe on No. 6, Ogilvy two-putted for birdie on the eighth, and the Australian birdied the ninth from 8 feet.
Casey did not make a birdie on the front nine, but he got back into the game with a 6-iron that covered the flag and rolled into the cup from 200 yards on the 10th hole.
Casey, who won the World Match Play Championship in England in 2006, twice had a chance to gain some momentum.
In a peculiar decision, Ogilvy went for the green on the par-5 11th and hooked his fairway metal into the desert. He found the ball stuck on a bed of jumping chollas, and he left it there so as not to prick his hand. He took a penalty drop some 20 yards back into the desert and still failed to reach the green.
Casey was in a bunker, but only able to advance far enough to leave him 262 yards for his third. He pulled that into a spot that left him no angle at the flag, and the best he could do was pitch to 20 feet.
Ogilvy, however, chipped in for par, Casey missed and the Aussie went back to a 4-up lead.
Oddly enough, the two finalists drove to Dove Mountain to play a practice round together two weeks ago. The 11th hole was the only one they did not play because another group was in front of them.
Casey won the 13th hole with a birdie, and then had a 7-foot birdie putt to cut Ogilvy's lead to 2 up, which would have given Casey a big left going to lunch. But he missed the putt, Ogilvy birdied the next hole from 15 feet, and the Aussie again was in command of the match.
Casey at least won the 18th hole with a 6-foot birdie, but he still had a big hill to climb in the afternoon.