SAN FRANCISCO – The benefit of standing on the sideline for the first 13 weeks of the NFL season: fresh legs.

Rookie LaMichael James displayed that Sunday, giving San Francisco's stop-and-start offense a bit of a boost as the 49ers eventually ran away from the Miami Dolphins in the second half and won 27-13.

With the win, the 49ers maintained their 11/2 game lead in the NFL West over the Seattle Seahawks, who also won Sunday, while also holding onto the NFC's No. 2 seed as the postseason draws near.

James, an elusive and electric player at the University of Oregon and the 49ers' second-round draft pick in April, hadn't been in uniform this year. But he was the first 49er to touch the ball Sunday, taking the kickoff deep in the end zone – where a returner might decide to kneel down – and bringing it out to the 26-yard line.

James said his NFL debut was not going to begin with a touchback – he was bringing the ball out no matter what.

"Delanie (Walker) said, 'Come on,' and I went," he said.

James also seemed to be a nice complement to Frank Gore's straight-ahead style in the 49ers' backfield. Anthony Dixon got into the game ahead of James in relief of Gore, but James gained 10 yards on his first carry and was Gore's primary backup for the rest of the game.

A week after he had a season-high 23 carries and a season-low 2.5-yard average, Gore ran the ball just 12 times – for 63 yards – against the Dolphins and went over the 1,000-yard barrier on the season for the sixth time in his career.

Gore scored on a one-yard run as the 49ers broke the game open in the beginning of the third quarter. His 19-yard burst up the middle at the start of the fourth quarter set up Dixon's one-yard score.

Jim Harbaugh called James' debut "fantastic," but the coach made sure it didn't eclipse Gore's afternoon.

"Frank Gore is also a tremendous back, if you hadn't noticed," Harbaugh said. "… Some great running throughout the game. Another great effort – blocking, everything that Frank does."

James also continued the nice rapport he began with quarterback Colin Kaepernick in the preseason.

The two played in wide-open college offenses, and that common background made them an easy fit on and off the field when James joined the 49ers in the spring. James even lived in Kaepernick's spare bedroom until the start of the season.

For the second straight week, the opposing defense took away Kaepernick's primary passing options, forcing him to go through his progressions. As a result, Kaepernick was sacked four times, three coming in the first half.

But as Harbaugh noted afterward, the quarterback again was accurate, completing 18 of 23 passes for 185 yards. And unlike last week in St. Louis, Kaepernick didn't make any crucial mistakes.

Harbaugh also made a point to compliment offensive coordinator Greg Roman, who was criticized heavily for calling the disastrous pitch-option play last week that contributed to the loss to the Rams.

"I thought Greg called a great game," Harbaugh said. "He always does. And we had a good plan. Our guys believed in the plan, and they executed it well."

Roman, in fact, called a read-option play three straight times as the 49ers tried to run out the clock at the end of the game. On first down, Gore gained three yards. On second down, Kaepernick ran for two. On third down, Kaepernick kept the ball again, this time bursting through the Dolphins' defense for a 50-yard touchdown.

After the game, James was asked whether an offense that features as many option plays as the 49ers' can have success in the NFL.

Said James: "It worked today."

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