Singh had his best round in six months, shooting a 7-under 63 on Thursday in the Greenbrier Classic to take a one-stroke lead over Maggert, Jonathan Byrd and Martin Flores – and leave Tiger Woods eight shots behind.
''Gosh, I don't know where that came from,'' the 49-year-old Singh said. ''I've been playing pretty good golf for a while, but just never got any scoring going. But today seemed I hit it close and drove the ball really well, hit a lot of greens and made some nice putts.''
Last week at the tough layout at Congressional, only seven players posted first-round scores in the 60s.
Sixty-two players broke par Thursday on the Old White TPC course, with the greens far more forgiving than last year when they were reseeded and Scott Stallings won at 10 under.
Woods wasn't one of them. Coming off a victory Sunday in the AT&T National, he struggled with his putter in a 1-over 71 in his final tuneup for the British Open in two weeks.
Saying the greens rolled slower than those in his last three tournaments, Woods needed 31 putts on the course he played for the first time Wednesday.
''I was a little bit off with my game, and on top of that I didn't have the speed of these greens at all,'' said Woods, the Tour leader this year with three victories. ''I missed literally every single putt high today.''
Singh had his best effort since an 8-under 64 in the first round of the Farmers Insurance Open at Torrey Pines in January.
Singh is playing in his ninth tournament in 10 weeks with two top-20 finishes in that span. Last week, he also got off to a fast start but shot 81 in the final round and tied for 49th.
Something clicked Thursday, when he made six birdies on the back nine, finishing with four straight.
''Hopefully it keeps going,'' Singh said. ''I don't feel tired. I feel really energized. I've been working really hard on my game, so it's nice to see something happen.''
Singh earned the last of his 34 PGA Tour wins four years ago and will be eligible to join the Champions Tour in February.
Maggert, a year younger than Singh, has had to earn his PGA Tour card through qualifying school in two of the last three years. He hasn't won since the 2006 St. Jude Classic and missed the cut in more than half his tournaments this year, including last week.
Although he feels he has a disadvantage off the tee compared with younger players on the 7,274-yard Old White, Maggert used strong iron play to make four birdies on his front nine.
Asked to describe his birdie putts, Maggert joked, ''At my age, it's hard to remember – short-term memory's going.''
He didn't need a big measuring stick – three of his six birdies overall were from less than 10 feet in a bogey-free round.
''I feel really comfortable here,'' Maggert said. ''There's a lot of guys out here in their 40s, late 40s, that can really play some good golf still. So it's not surprising to see some of the old guys up on the leaderboard.''
Byrd has five career wins and already has five top-10 finishes this year. He hadn't played since the U.S. Open and fought through a nagging cough to finish birdie-bogey-birdie Thursday.
Flores had a rare bogey-free round that was his second best of the year. He spent the majority of 2011 on the Nationwide Tour, now called the Web.com Tour.
On the par-5 17th, he drove into a hazard, took a penalty stroke and three-putted from 20 feet for double bogey.
Phil Mickelson matched Woods with a 71. Mickelson vowed to focus more on golf this time after taking advantage of the resort's numerous amenities with his family last year and missing the cut.
''I didn't play that bad (Thursday),'' Mickelson said. ''But I made some mistakes there that were just a little sloppy.''