The 12-year-old birdied both 14 and 15 at the Morgan Run Club & Resort, in Sante Fe, and would have finished inside the top six had fortune smiled on him on the final three holes.
He lipped out for birdie on both 16 and 18 and left his birdie putt at 17 on the edge of the cup to place in a tie for 13th.
The Brighouse High pupil produced consistent scores of 71 72 71 for a two-under-par aggregate of 214.
New Zealand’s Joshua Bai enjoyed a one-shot victory after rounds of 66 68 71.
Walsh commented: “It was a tough course when the wind was up. I really enjoyed it although it would have been better had a few more putts dropped.
“It’s been a great experience and I’ve met loads of new friends from all over.”
On day one Walsh birdied at the first, but was one over at the turn after dropped shots at five and eight.
Consecutive birdies to start the homeward run got him back below par, and after dropping a shot at 13 he immediately birdied 14 before a four-hole par run to the clubhouse.
Round two saw him start with two birdies and, despite a bogey at three, he was under par through nine. He sandwiched a birdie at 14 with bogeys at 12 and 15.
Some great up-and-downs resulted in a one-under-par 71.
His father Lee said: “Louie played amazing, I’m so proud.
“He was one over with five left in his last round, but I said, ‘come on, play your best ever’.
“He went birdie birdie, lipped out for birdie on 16, put it to seven feet at 17 and his putt for birdie stopped on the edge, and he lipped out again from a great tee shot to six feet ath the last.
“Unbelievable. Those would have given him top six, but that’s golf.”
Walsh qualified for the prestigious tournament at the British Junior Golf Tour qualifier at Park Hill GC last September.
The qualifier for next year’s IMG Academy Junior World Championships takes place on September 23 at Cambridge Meridian, with over 120 juniors from around the UK signed up to compete for the places to represent the UK in San Diego next year – and another 80 are on the reserve list.
The sole aim of the British Junior Golf Tour, a not-for-profit company, is to increase the opportunities for young golfers to show just how good they are.
As one of the few organisations in the UK to promote the use of caddies, the BJGT is encouraging families to come out and enjoy the game together.
To learn more about the BJGT and to sign up to play on the Tour, please visit www.juniorgolftour.co.uk