The reigning Australian PGA champion began the final round four shots off the lead of Bryson DeChambeau but with an eagle-birdie start was within one before the American teed off.
However, he ended up 10 from the lead after a series of back nine mis-steps saw him sign for a 3-over 74.
A bogey at the par-4 third was hardly disastrous but the setback seemed to kill Smith’s momentum as he reeled off a frustrating run of six straight pars to turn 2-under.
Still within three at that point he was far from out of the mix but wayward driving over the closing nine holes was to prove disastrous.
At the 10th hole he drove it in the water and made a double bogey which was compounded by another errant drive at the next for a second straight double.
With four shots gone in two holes Smith tumbled down the standings but there was more to come, a birdie at the par-3 14th offset by a third double bogey for the day at the par-5 15th.
Again, it was an errant tee shot that proved fatal as he took two swipes to get back to the short grass after missing the fairway right.
An inward half of 40 added up to a 3-over 74 and at 3-under for the week Smith is now 10 shots off the pace.
After an outstanding performance to finish T5 at Augusta National last week, today’s difficulties will be particularly disappointing for the 24-year-old who is in search of a second PGA Tour title this year.
Smith wasn’t the only player to struggle, however, overnight leader DeChambeau paying the price for an overly aggressive play at the second which cost a triple bogey and wracking up two doubles at 13 and 17 to slip to a share of 20th.
Houston Open winner Ian Poulter is now the leader by one at 13-under ahead of Players Championship winner Si Woo Kim and American Luke List. C.T. Pan and Billy Horschel share fourth at 11-under.
Rod Pampling is the best of the Australians heading to Sunday in a share of 36th place after his best round of the week Saturday, a 4-under 67 which moved him up 22 places in the standings. Aaron Baddeley is T61 at 1-under for the week.
SIGNATURE HOLES - 14TH EAST AT THE GRANGE:
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