Peter Jacobsen, who won last year's Senior Players Championship, posted a 4-under-par 67 and is alone in second place.
Three-time winner this season Loren Roberts carded a 3-under-par 68 and is tied for third place with 2001 champion Tom Watson and two-time winner in 2006 Jay Haas.
Perhaps some local knowledge helped the leader.
Morgan, who lives within a mile of the course, started on the back nine Thursday and immediately broke into red figures. He hit a wedge to 5 feet at 10 to set up his first birdie of the round.
He dropped a shot two holes later when he missed the fairway, then missed the green with his second. Morgan, a 23-time winner on the Champions Tour, parred his next two, but went on a run at the end of his first nine.
At the 15th, Morgan hit an 8-iron to 15 feet and converted the birdie putt. He made it two in a row at the par-5 16th when he missed the green with his second shot, but chipped to 3 feet to set up another birdie.
Morgan closed out his opening nine holes with a 4-foot birdie putt at No. 18.
'Starting out today, I was somewhat apprehensive with my start,' admitted Morgan. 'Made a birdie on my first hole. That kind of eased things up a little bit.'
Morgan parred one and two, but took advantage of the par-5 third. He laid up with an 8-iron, then wedged his third to 2 feet. Morgan kicked in the short birdie putt to reach 4 under par.
Morgan saved a nice par at the sixth hole when his approach skipped through the green. He chipped his third to 10 feet and drained the par putt to stay at minus-4.
He separated himself from the pack at the seventh. He hit a solid drive in the short grass, then Morgan played a gap wedge to 12 feet. Morgan sank the birdie putt to get to 5 under par, but needed one more par save to keep the first-round lead.
At the ninth, Morgan tried to avoid the false front on the green with his approach. His ball sailed well past the flagstick and his long birdie try came up 6 feet short. Morgan rolled in the par putt to stay one clear of his playing partner, Jacobsen.
'It's great to be able to play with great players and when they play well, it kind of spurs you or inspires you to play better,' said Morgan. 'All in all, it was a pretty good round.'
Jacobsen broke into red figures with a birdie at the 12th when he ran home a 15-footer. He dropped a shot at the 14th thanks to a three-putt, but looked poised for an eagle at the 16th. Jacobsen knocked a 5-wood to 15 feet, but his eagle putt hung on the edge. He tapped in for birdie to make the turn at 1-under 34.
Jacobsen, whose only two Champions Tour victories came at major championships, parred his first four holes on the second nine, then went on a birdie run to get within one of Morgan.
At the par-5 fifth, Jacobsen laid up, then hit a wedge to 3 feet and tapped in for birdie. He was inside a foot with his approach at six for another birdie, then he made it three in a row with a 25-footer at the par-4 seventh.
Jacobsen parred the next two to stay in second place.
'I drove the ball well and hit a lot of greens,' said Jacobsen, who won the 2004 U.S. Senior Open and the 2005 Senior Players Championship. 'Overall, I played well.'
Two-time U.S. Open champion Curtis Strange, Jim Thorpe, Craig Stadler, Katsuyoshi Tomori, two-time winner this season Brad Bryant and reigning Champions Tour Player of the Year Dana Quigley are knotted in sixth place at 2-under-par 69.
Defending champion Mike Reid, who defeated Quigley and Jerry Pate in a playoff last year, opened his title defense with an even-par 71. He is part of a group tied for 20th place.