Stephen Ames (71) and Paul Gow (69) share third place at 9-under-par 135, followed by Jonathan Byrd (70), Dicky Pride (70), Tom Carter (66) and Tom Byrum (68), who are tied for fifth place at minus-8.
Maruyama started on the back nine Friday and parred his first three holes. After that Maruyama went on a birdie tear, starting at the 13th when he drained a 12-footer.
He added an eight-foot birdie at the 14th, a tap-in birdie at 15 and completed four birdies in a row with an amazing second shot at the par-4 16th. Maruyama nailed a 4-iron into the wind from 204 yards to three feet to set up birdie.
Maruyama dropped his first shot of the tournament at the 18th but his play on the front nine extended his lead. At the first, Maruyama hit a sand-wedge that spun to 20 feet but he canned the putt for his fifth birdie of the round. He made it two in a row at the par-five second when his second missed the green short but his chip stopped a foot from the cup.
Maruyama once again used fine wedge play to make birdie. At the fifth, his sand-wedge from 95 yards stopped three feet from the hole to set up birdie. He birdied the seventh and knocked his third to two feet at the par-5 ninth to miss Jesper Parnevik's 1999 36-hole record by a shot.
'I knew I was leading and I was just trying to get another stroke lead,' said Maruyama, referring to his play at No. 9. 'I was happy and excited to finish the round that way.'
Maruyama has struggled since a neck injury hampered his play the last two years. He hasn't won since the Byron Nelson Classic last season but a change in clubs has brought him back to his old form.
'I changed to a lighter club, a lighter shaft, actually,' said Maruyama. 'Tiger Woods, the big players, they are using the same shaft as I used to use, so I got a lighter shaft for my swing.'
Faxon was 1 under par after a bogey at No. 10 but his play after the hiccup propelled him into second place. He knocked an 8-iron to 10 feet to set up birdie at the 11th, then made it back-to-back birdies with an 18-footer.
At the 14th, Faxon hit a 7-iron to seven feet for birdie and closed his round of 5-under 67 with a tap-in birdie at the par-5 15th.
Faxon was philosophic about his chance of catching Maruyama.
'If he shoots 15 more under I don't think he can be caught,' admitted Faxon, a Red Sox fan who donned their cap during Friday's round. 'Who knows? Certainly five shots is a big lead after two days, but we're only halfway.'
Peter Jacobsen, the overnight leader, struggled to a 2-over 74 on Friday. He is tied for ninth place with Geoff Ogilvy (69), Dave Stockton, Jr. (69), K.J. Choi (69), Per-Ulrik Johansson (66), Jay Haas (68), Matt Gogel (67) and David Sutherland (66). That group stands at 7-under-par 137.
David Toms, a two-time winner this season on tour, was tied for third place after Thursday's opening round but, like Jacobsen, played poorly on Friday. He shot a 2-over 74 and is part of a group tied for 24th place at 5-under-par 139.
The 36-hole cut fell at 1-under-par 143 and the biggest player to miss the cut was Davis Love III. Love, a four-time winner in 2003, shot a 2-over 74 on Friday and missed the cut at even-par 144.
What makes Love's missed cut even worse is that Love did re-design work on Forest Oaks Country Club this winter, including significant work on all 18 greens.