Greg Norman, one stroke short of victory in his last two tournaments, completed a 64 with an eagle on the 18th hole and opened a three-shot lead today after four rounds of the richest tournament on the PGA Tour.

Norman, who said he has had a case of walking pneumonia for about a year, completed 72 holes of the five-day, 90-hole Las Vegas Invitational in 268, 20 strokes under par.

On the 18th, Norman's drive covered 340 yards. A 3-iron second shot stopped 15-18 feet from the cup and he rapped it in for an eagle.

The winner's share is $207,000 from a total purse of $1,150,000.

Second at 271 after a 66 was Dan Pohl, playing with his left thumb taped because of a sprained ligament. Pohl made three straight birdies at the turn and had no bogeys.

Bob Tway, Dave Rummells and Larry Nelson were next at 272. Tway had a 68, Rummells and Nelson 69.

Former Frederick, Md., golfer Donnie Hammond, who could collect a $250,000 bonus if he coupled a victory here with the Bob Hope Classic title he won earlier in the season, slipped out of the lead with a 73 and was seven off the pace at 275.

Norman said of his ailment, "I've had it about a year . . . I'm taking medication for it, but the medicine makes me lightheaded. So I've cut back to some half-strength medication this week. I'm taking two weeks off after this tournament and I'm going to see a doctor in Houston and see if we can't get it cleared up."