James Mason and Dave Eichelberger share second place at 2-under-par 70, followed by Tom Jenkins, Andy Bean and Vicente Fernandez, who share fourth place at 1-under-par 71.
Canizares wasted little time going into red figures. He knocked his approach to three feet to set up birdie at the first and collected back-to-back birdies with a tap-in birdie at the par-5 second hole at The National Golf Club of Kansas City. Canizares made it three birdies in a row with a two-footer at the third.
The Spaniard three-putted the fourth green for a bogey but responded in a big way. He played a wedge to three feet to set up birdie at the fifth and hit a 6-iron to the same distance at the sixth for his fifth birdie in six holes.
Canizares once again followed a birdie run with a bogey. He missed a six-foot par save at the seventh before four pars in a row as he made his way around the turn.
Canizares missed a three-foot par putt at the 12th but rebounded with a tap-in birdie at the 15th.
'I started very good and then played okay from then on,' said Canizares, who won the 2001 Toshiba Senior Classic. 'The rain was coming very heavy at times and the wind was tough. The course held up pretty good. The water drained pretty quickly.'
The 3-under-par 69 Canizares shot on Friday was the highest opening-round score for a leader on the Champions Tour in 2003.
Mason collected four birdies and one bogey before he reached the closing hole. He three-putted the par-5 18th for a rare bogey at the finishing hole to drop one behind Canizares.
'I'm very happy with the round,' said Mason. 'The conditions were tough. The course was much harder than in the practice rounds. It's going to be important to have it in the fairway here this week.'
Eichelberger made the turn at even-par but dropped a shot at the 11th when he drove the ball in the right rough. He atoned for the mistake at 11 with three birdies in his last six holes, all from inside of six feet.
'I hit the ball better than I have all year,' said Eichelberger. 'I'm very encouraged by my play. I got a big break being in the last half of the field. The weather was rougher earlier.'
Ed Fiori, Jay Sigel, Allen Doyle, Andy North, Wayne Levi, Butch Sheehan and course designer Tom Watson share seventh place at even-par 72.
'I'm grinning ear-to-ear,' said Watson, referring to his course which yielded a 75.384 scoring average on Friday. 'I thought the conditions were perfect today. You have to take what the wind gives you.'
Bruce Lietzke will not be able to defend his title. He withdrew on the 14th hole Friday with tendinitis in his elbow.