Stricker said maybe it was because it's been a while since he played in a major. He has gone three years since his last victory, the British Open at Muirfield, where his 66 ranks among the great closing rounds in a major.
And it might be his last major. He bogeyed the first hole after hitting his driver a long way right.
Not even close. Mickelson tied the lowest round ever at an Open Championship and shot just the second 63 at an Open since 1993 (although just one of those players, Greg Norman in 1986, went on to win the tournament).
Americans dominated the leaderboard Thursday.
On No. 11, the Railroad Hole, the most hard on the course, Spieth said his drive was on a good line, but got caught up in a bush. The last was by Rory McIlroy in 2010 at St. Andrews. He threw his arms up in celebration for what was his second hole-in-one at a major this year, after acing the 16th in the final round of the Masters. On the 18th hole, he left his approach shot short and left to a front-left hole location, leaving a almost impossible up-and-down for par.
Montgomerie was given the honor of hitting the first tee shot at Royal Troon, his home club, in what likely will be his last Open. It was a proud moment for the 53-year-old Scotsman but things quickly turned sour.
Texan Reed, 25, signalled his intent when he holed his approach shot for an eagle two at the par-four third.
He recovered from a double-bogey six at the first to shoot a respectable 71.
NOT SO FAB FOUR: The top four players in the world were a combined even par. He says "I'm very proud of myself for hanging on in there. It would have been easy to score 78 there, simple". A lone birdie on 15 was the only bright spot on his back nine.
For the start of the 145th Open, there was no wind at all.
Mickelson was five under through 10 holes and Leonard four under through 13.
Meanwhile, Day struggled early and had three bogeys on the front nine.
It was still good enough for an eight-under effort and a bogey-free round, and it put him three ahead of compatriot Patrick Reed and Martin Kaymer of Germany.
But in recent years, age hasn't been much more than a number at the Open Championship.
Colin Montgomerie found that out.
Spieth navigated Troon's 7,190 yards with little difficulty, other than errant drives that led to bogeys on holes 11 and 18. Alas, Monty couldn't keep it going.
Mickelson's round included birdies at Nos.
Most encouraging of all: The lead threesome took just under two hours to complete the front nine.
The 2016 Open Championship is underway, and already the tournament is not what many have expected.
However, high scoring on the inward nine has proved a theme at Troon, and the American suggested overconfidence from a strong start could be an issue. He might want to heed his own advice.
"It's just a good feeling coming to the Open knowing that I can play Open championship golf".
Prestwick, site of the first 12 British Opens, is adjacent to Royal Troon.
Adam Scott, desperate to get his hands on the elusive Claret Jug after four painful near misses in the past four years, tees off just before 2am (NZT). Five dogs were on the beach, running along the shores amid tall shadows cast by the rising sun.