By the numbers: History not on Walker's side

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Jimmy Walker went out early on Day 1 of the PGA Championship and put up a 5-under 65 that no one in the field could match. He leads the trio of Emiliano Grillo, Ross Fisher and Martin Kaymer by one shot while other big names like Dustin Johnson, Phil Mickelson, Sergio Garcia, Bubba Watson and Rory McIlroy all finished over par.

Here are the key stats from the first round at Baltusrol:

 Walker's 65 tied his lowest career round in a major. In his 10 major rounds before Thursday, he was a combined 32 over par.

 No major winner this year has led after the first round. Danny Willett was four shots back at the Masters, Johnson trailed by one at the U.S. Open and Henrik Stenson was five behind at The Open.

 Over the past 30 PGA Championships, only four winners have lead or co-lead after Round 1 and 50 percent of winners were outside the top 10 after 18 holes.

• Kaymer (68) is vying to become just the third European player (Seve Ballesteros and McIlroy) in the modern era to have won three majors at 31 or younger.

• Henrik Stenson shot a 3-under 67. He is 36 under in majors since beginning of 2013 (best in span) and with a win would join Ben Hogan as the only players over the age of 40 to win consecutive majors.

• Rickie Fowler tied his lowest career first-round score in major with a 68. He was a combined 25 over in first rounds of his previous seven majors.

Jason Day still has a shot to defend his PGA title after a first-round 68. If the Aussie could pull off a victory this week, he would join Padraig Harrington and Tiger Woods (four times) as the only men to successfully defend a major title since 1995.

• Day hit a major career-high 17 greens in regulation on Thursday. Unfortunately, he made only two putts longer than 6 feet.

• Mickelson (71) shot 67 in the opening round of his PGA win at Baltusrol in 2005.

• McIlroy failed to make a birdie on Day 1, marking the first time he hasn't carded a circle in his PGA Championship career and fourth time in any major.

Note: Golf Channel’s editorial research unit contributed to this report.