Marsh, who also led after the first round of this year's Senior PGA Championship, jumped out of the gate at the par-4 first after his second shot stopped 3 feet from the hole. Marsh added a birdie at the par-5 third and dropped his tee shot inside 2 feet for a birdie at the par-3 fourth.
'If you're on with your short game, which I happened to be earlier this morning with the wedges and so forth, I was able to get them in close,' Marsh said. 'A lot of those were kick ins. All of a sudden you make a couple of long putts, you're up and sailing.'
The Australian played his approach to 8 feet for a birdie at the par-4 sixth. but three-putted for a bogey at the very next hole. Marsh responded with a birdie at the par-3 eighth to make the turn at 4 under.
Marsh continued his fine play on the inward half and picked up the first of three consecutive birdies at the par-4 11th after his approach came to rest 6 feet from the hole. He then knocked his tee ball within 15 feet for a birdie at the par-3 15th and rolled in an 8-foot putt for a birdie at the par-5 17th to get to minus-9.
The 61-year-old, whose last Champions Tour victory came at the 1999 Tradition, suffered a bogey at the closing hole, but the slew of birdies he picked up before was more than enough to secure the opening-round lead.
'The golf course is in absolutely superb condition. It was there for the offering this morning,' said Marsh. 'It's the kind of golf course that is very much orientated towards target golf.'
Watson ran off birdies on each of his first three holes and moved to 4 under with a birdie at the seventh. He stumbled to a bogey at the eighth, but recovered with a birdie at the 11th.
He followed that up with a birdie at the par-5 13th and added a birdie at the 15th to get within two of the lead.
'I hit the ball pretty close to the hole all day,' said Watson. 'It was an easy day to score. The wind wasn't blowing. The TPC of Dearborn, when the conditions are soft like this, if you're driving the ball half decently, you're going to do pretty well.'
Aoki, who tied for second at this event in 1997, collected back-to-back birdies from the second, but found trouble with a bogey at the fourth. Aoki countered with a birdie at the fifth and two straight birdies starting at the seventh to go out in 32.
The 62-year-old from Japan added a pair of birdies on the back nine to join Watson in second place.
Streck earned his first Champions Tour victory last week at the Commerce Bank Championship and has carried that momentum to the Senior Players Championship. Streck birdied three of his first four holes and added another birdie at the par-4 ninth.
The 50-year-old birdied the 12th and converted a 6-foot birdie putt at the 13th to move to 6 under. Streck bogeyed the 14th, but responded with a birdie at the 15th.
Jerry Pate, Andy Bean, Larry Nelson, Bruce Fleisher, Morris Hatalsky, Don Reese, Gary McCord, Tom McKnight and Hale Irwin share eighth place at 4-under-par 68.
Defending champion Mark James is six shots off the pace after a round of 70.