"I hit it really well, but hooked it and it landed just on the green and ran up," McKenzie said. "I holed that coming down the hill. So that was making the most of a bit of luck."
After tying for second last week in the Fiji International, McKenzie qualified for the Boeing field Tuesday in a playoff.
"I was probably a little bit nervous teeing off, but overall I sort of struck the ball pretty well," McKenzie said. "First couple of holes was a little bit of a battle-fest, but sort of got into a bit of rhythm and made a few putts."
He tied for ninth in the Senior British Open in his first senior start.
Kelly had eight birdies and a bogey. The three-time PGA Tour winner is making his 13th senior start after turning 50 in November.
"I haven't had a good tournament yet," Kelly said. "I'm hoping this is the first one."
Marco Dawson and Duffy Waldorf were a stroke back.
Dawson had seven straight birdies, falling a hole short of the tour record. Playing the back nine first, he birdied Nos. 14-2. He had a double bogey on the par-4 fourth and birdied the eighth.
Waldorf had five birdies and a bogey on the final seven holes.
Stephen Ames and Scott Parel shot 67, and Vijay Singh was at 68 along with Bob Estes, Rocco Mediate, David Frost and Jerry Smith.
Defending champion Bernhard Langer had a 70, and Scott McCarron shot 71. Langer also won the 2010 event. He has a tour-high four victories this year, winning three of the tour's five major championships. McCarron won the Dick's Sporting Goods Open on Sunday in New York for his third victory of the year.
Local favorite Fred Couples opened with a 72.
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