EARTH CITY, Mo. — After the 2013 season ended, it looked like the St. Louis Rams had the running back they could build around coach Jeff Fisher’s run the ball and play good defense philosophy.

Then-rookie Zac Stacy had just one rushing attempt in the first four games of that season but finished the year with 973 yards.

Now, Stacy is mostly a forgotten man as another rookie, third-round pick Tre Mason, has won the starting job, also after being an after-thought at the beginning of the season.

In fact, Mason was inactive for the first four games before getting his chance and taking advantage of it. Starting the last five games, Mason now has 562 rushing yards and is averaging 4.6 yards per attempt, better than Stacy’s 3.9 average last season.

Mason has two 100-yard games, but most important, brings big-play opportunities to the offense. Fourteen of his 122 rushing attempts have been for 10 yards or more, and six have been for 21 yards or more, including an 89-yard touchdown run against the Oakland Raiders.

“He gives us the explosives,” offensive coordinator Brian Schottenheimer said. “And he’s got really good instincts. The more he carries it, I think he starts to see the cuts develop, can pre-snap some things. See the safeties, how they start to fill.

“Again, he’s just getting better and better. What we like about it and have noticed more and more is just how strong he is. (Against San Diego), he had a couple one-on-ones with a safety and he broke or ripped through the tackle. I think that’s been a pleasant surprise for us.”

Like the entire team, Mason has to find a way to string good games together. He had 113 yards in a win over Denver then 62 in a loss to San Diego the following week. Then came the 117-yard game against Oakland, highlighted by the 89-yard lightning bolt.

Also credit Mason for being something of a soothsayer.

Fisher explained, “He said he was gonna have a big day. He guaranteed me that before the game — and he did.”

Mason added, “I told the team before we went out there: ‘Let’s get 50-plus today.'”

They did that, too, with Mason contributing three touchdowns, one of which was a 35-yard screen pass that he turned the corner and blew past a few Raiders that had angles.

Of course, there’s more. With the Rams on the 11-yard line and leading 21-0, Mason said, “Before that long run, I told Shaun (Hill) I might break this one.” And he did.

“It happened twice, so I don’t know what was up with me,” Mason said.

Linebacker James Laurinaitis said, “I don’t know if he’s a prophet. But goodness, what a prediction.”

Of course, Fisher let it be known that Mason has been brash in his projections before. “It’s not the first time he’s said it,” Fisher said. “So he’s very confident. He loves to play.”

Mason also revealed there might have been another reason for his big afternoon.

“They told me I was miked up, so I had to give them a good show,” he said.