The 21-year-old signing from Falkirk put Huddersfield on their way to a third league win with a stunning early strike.
It was the Scottish Under-21 international's first goal for the Terriers after signing last month and it helped lift Huddersfield into fourth place, just a point behind new leaders Peterborough.
"Scott is going to be a terrific player. We're not even seeing him in his real position and he's doing brilliantly," said Clark.
"He's had spells at right-back and as a right-wing back and he just gets on with it – he's a manager's dream.
"I knew when we tried to get him in the summer we would have a very good player on our hands. I said he was one of the brightest young prospects in Scottish football and I think our fans are seeing that."
After Arfield's opener, Terriers substitute Jordan Rhodes looked to have wrapped things up with his fifth goal of the season 12 minutes from time.
But Dean Cox netted for Orient 60 seconds later to set up a thrilling finish and Huddersfield had to defend well to hang on to maximum points.
Clark believes more of those battling displays are needed to go up: "I've just told my players that if you are going to win a Championship we will probably need nine or 10 of these performances where we dig in and all stick together away from home," he said.
Leyton Orient: Jones; Omozusi, Chorley, Forbes, Frampton (Smith 46 mins); Chambers, Spring (Jarvis 76 mins), Dawson, Cox; McGleish (Walker 86 mins), Revell. Unused substitutes: Butcher, Brown, Porter, Cestor.
Huddersfield Town: Smithies; Arfield, McCombe, P Clarke, Ridehalgh; Roberts, Johnson, Kay, Carey (Gudjonsson 72 mins); Garner (Novak 57 mins), Lee (Rhodes 63 mins). Unused substitutes: Bennett, Croft, Atkinson, Chippendale.
Referee: Andy D'Urso (Essex)
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