Kolby Smith knows the NFL is not this easy, that it’s not some video game, set on the beginners level where fifth-round draft picks gain 150 yards in their first start.

Oh, yes, Smith knows not to be disappointed if he falls a bit short of that today, or any other game he starts from here on out.

But just in case, veteran Eddie Kennison is willing to step in. Quick and easy, too.

“I’d pull him in my office, do him like I do my 9- and 5-year-olds,” Kennison says. “Grab him by the collar and talk to him. A hundred yards would be good. Heck, 56 would be good if it came with a win.”

Thing is, nobody can be really sure what to expect from Smith. His name sounds more like an X-Gamer than a football star, yet here he is, front and center in the Chiefs’ plans for today.

It’s a head-spinning position for Smith, from third-stringer and special-teamer at the beginning of the season to a popular pickup in fantasy leagues and the featured back in a ball-control offense.

But you know what else? It’s not all that unfamiliar to Smith. The guy never started in college until — ahem — an injury to the running back ahead of him on the depth chart.

So Smith isn’t freaking out about any of this, and most of all, he’s not thinking he’s hot stuff just because he had a big game against the Oakland Raiders.

“That’s just one game,” he says. “I gotta get a couple games under my belt before I start talking like that.”

Smith is used to being overlooked. It started in college, and not just because he was a running back in Bobby Petrino’s pass-happy offense at Louisville. Smith shared time and attention with Michael Bush, Lionel Gates and Eric Shelton, all of whom have since been with NFL teams.

But it is worth knowing that his senior year, when Smith became the starter after Michael Bush went down with an injury, he finished the season with 862 yards in 154 carries, a 5.6 average.

Matter of fact, Michael Bush himself proved something of a fortune teller when he sensed Louisville fans panicking about his season-ending broken leg.

“I think a lot of people may be sleeping on Kolby,” he said then. “You’re going to see a lot of big plays out of him.”

Smith is the cousin of Bears safety Mike Brown and Colts receiver Craphonso Thorpe, and athleticism has never been the issue. He’s not particularly fast (4.5 seconds in the 40-yard dash) but has measured a 40-plus-inch vertical leap.

The knocks have been durability (he missed parts of both his sophomore and junior years with injuries) and elusiveness.

But his first big game against the Oakland Raiders certainly caught the attention of Chargers running back LaDainian Tomlinson.

“Anytime you’re a young player and you have that kind of success your first game starting, it does give you confidence you can get it done in this league,” Tomlinson said. “I’m sure Kolby’s going to try to build on that success he had last week. That’s what this league is all about.”

Then again, it wasn’t all touchdowns and highlights for Smith in that first start. It would’ve been if he’d gained 151 yards, but he missed on that last carry, getting stuffed on a fourth-and-1 that essentially ended the Chiefs’ chances.

Chiefs coach Herm Edwards (half) joked that Smith would’ve been thrown a parade if he’d made that last yard, and Smith said last week that he’d remember his first start more for the yard he didn’t get rather than the 150 he did.