Luke Donald shot a sparkling eight-under-par 64 on the first day of the Memorial tournament to take a three-shot lead.
The Briton started his round with a bogey at the first but a run of six birdies in seven holes on the back nine propelled him up the leaderboard ahead of Americans Jim Furyk and Ted Purdy, Australia's Jason Day and South Africa's Thomas Aiken, who all carded opening rounds of 67.
It was the lowest score of Donald's PGA Tour season so far and having picked up eight shots in nine holes from the eighth.
"I just got on a hot streak," he said. "Eight under through nine holes, that doesn't happen very often but when you get on that roll, it feels pretty good. So I just kept going and made some birdies."
Purdy carded seven birdies but shipped a costly double bogey at the par three 12th, while Day finished with back-to-back bogeys.
Steve Marino, Stewart Cink, Mark Wilson sit tied for sixth at four under, with group of nine including world number one Tiger Woods, who has won the title three times at Muirfield Village Golf Club, tied for ninth a further shot back.
Elsewhere, Open champion Padraig Harrington struggled to a three over 75 alongside Vijay Singh.
Collated first-round scores (USA unless stated, par 72):
64 Luke Donald (Eng)
67 Thomas Aiken (Rsa), Jim Furyk, Ted Purdy, Jason Day (Aus)
68 Steve Marino, Stewart Cink, Mark Wilson
69 Tiger Woods, Rodney Pampling (Aus), Kevin Sutherland, Mike Weir (Can), Reinier Saxton (Ned), Johnson Wagner, Troy Matteson, Jonathan Byrd, Nicholas Thompson
70 Will MacKenzie, Steve Stricker, Ernie Els (Rsa), Ryuji Imada (Jpn)
71 Charley Hoffman, Zach Johnson, John Senden (Aus), Tom Lehman, Ben Curtis, Bubba Watson, Martin Kaymer (Ger), David Duval, Matt Bettencourt, Tom Pernice Jnr., Chez Reavie, Kevin Na, Camilo Villegas (Col)
72 Michael Letzig, Jerry Kelly, Charl Schwartzel (Rsa), Erik Compton, Davis Love III, Lee Janzen, Geoff Ogilvy (Aus), Kenny Perry, Daniel Chopra (Swe), Robert Allenby (Aus), Mark Calcavecchia, Marc Turnesa, Stuart Appleby (Aus)
73 Nick Watney, Bart Bryant, Todd Hamilton, James Nitties (Aus), Nick O'Hern (Aus), Webb Simpson, Shaun Micheel, Y.E. Yang (Kor), Chris DiMarco, Steve Flesch, Matt Kuchar, Alex Cejka (Ger), Paul Casey (Eng), Dustin Johnson, Mathew Goggin (Aus), K J Choi (Kor), Rocco Mediate, Carl Pettersson (Swe), D.J. Trahan
74 Scott McCarron, Billy Mayfair, Greg Owen (Eng), Jose-Maria Olazabal (Spa), Hunter Mahan, Brett Quigley, Bill Haas, Marc Leishman (Aus), Richard Sterne (Rsa)
75 Tim Herron, Mark Brooks, Lucas Glover, Jeff Quinney, Woody Austin, John Mallinger, Charles Howell III, D.A. Points, Vijay Singh (Fij), Ian Poulter (Eng), Padraig Harrington (Irl), Ryan Moore
76 Jeff Overton, Steve Lowery, Jeff Klauk, Billy Andrade, Richard S Johnson (Swe), George McNeill, Sean O'Hair, Tim Petrovic, Ken Duke
77 Charles Warren, Chris Stroud, Adam Scott (Aus), Jason Dufner, James Driscoll, Kevin Streelman, Peter Lonard (Aus), Fredrik Jacobson (Swe), James Kamte (Rsa)
78 Brian Davis (Eng)
79 Chris Wilson, Danny Lee (Nzl), Aaron Baddeley (Aus), Scott Piercy, Cliff Kresge
80 John Rollins, Justin Rose (Eng), Ryan Palmer
81 Bo Van Pelt, Parker McLachlin, Jesper Parnevik (Swe)
82 J.B. Holmes
83 Brad Faxon
86 Kevin Chappell
Report: Green Bay Packers receiver Donald Driver seeks reworked contract
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