The American was in good form as he backed up his 18th hole eagle with four birdies to move two shots clear ahead of the chasing pack.
Crocker, who was also the halfway leader, completed a third round 69 as he displayed brilliant patience despite the testing conditions at Fairmont St Andrews.
The 25-year-old is targeting his first DP World Tour title as he looks to capitalise on his return to form. The player started the season by missing nine cuts in succession, but appears to be back on track.
He said: "It's nice to have a bit of room but I also know those gaps can be closed very quickly.
"I've just got to play my own game tomorrow and see what we can do.
"It would probably be the most special day of my life (to win this week).
"I play golf for the love of it, for trophies and all that stuff. It's been a long time since I've held something shiny so it would be a nice little present."
Jens Dantorp was Crocker's nearest challenger on 16 under, with Scotland's David Law and Spaniard Adrian Otaegui another stroke behind in a tie for third.
Welshman Oliver Farr and England's Eddie Pepperell were in a share of fifth place on 14 under.
Englishman Graeme Storm had a day to remember after securing a hole-in-one at the difficult 17th hole to claim the £20,000 prize.