After being inactive for the first 12 games of the season, James has become an impact player for the 49ers in their run to the season's finale next week against the Baltimore Ravens.
His long kick-off return set up the crucial score in a late-season win against the New England Patriots. And his experience at reading the running plays in the zone helped his quarterback Colin Kaepernick rush for 181 yards in the play-offs victory against the Green Bay Packers.
Then James got into the scoring act himself last week, starting San Francisco's comeback in a 28-24 win at the Atlanta Falcons in the NFC Championship game.
"I had a lot to learn," James said.
"I'm still learning."
Fresh from scoring his first professional touchdown in last week's win over the Falcons, James is finally fulfilling the expectations the 49ers had for him after drafting him in the second round last April following a stellar college career at Oregon.
"From the first time he stepped on the field, he's been dynamic," said Jim Harbaugh, the 49ers coach.
Getting on the field was the hard part. James had to learn a much more extensive playbook than he was used to at college. He dutifully worked at learning his craft, making his contributions as a scout team running back and receiver, and soaking in whatever tips he could get from the starter Frank Gore and the running backs coach Tom Rathman.
"It was very different," James said.
James got his chance after Kendall Hunter went down with a season-ending Achilles injury in the game against the New Orleans Saints in November. The 49ers needed a change-of-pace back to team up with Gore and James proved to be a perfect fit. He was helped by the fact that the 49ers offence had changed a bit with the switch at quarterback to Kaepernick from Alex Smith, with the team using more of the read option plays James was so proficient at in college.
"Once he started getting comfortable, we saw a dynamic football player," the safety Donte Whitner said. "It's a testament to him to be able to sit on the sideline and be on the developmental squad, as we like to call it, here for so long and actually knowing that you can play football.
"Actually coming from a big university, playing in a lot of big games and being a big-time player, and having to sit out and be humbled like that, that's a testament to him and the character he has."
James rushed for 5,082 yards and scored 58 touchdowns in three seasons for Oregon. He played in three major college bowl games, including the national final two years ago.
"I don't think there's too much difference from playing a bowl game at Oregon," James said of the NFL play-offs. "I think it's really helped me out playing big games like these. It's second nature to me. I really don't think it's too big a deal."