The San Francisco 49ers offense was a bit stuck on Sunday night against the Dallas Cowboys, but an unlikely hero helped them turn things around.

The 49ers scored just six points in the first half of a 30-24 win over the Cowboys. Their running game in particular struggled, as running back Jordan Mason only managed 18 yards on six carries in the first quarter and transition.

A shoulder injury eventually forced Mason to the locker room before halftime, opening the door for fourth-round rookie Isaac Guerendo. He came into the game with just 23 runs scored on the season, including just one in Week 7 against the Chiefs.

Sunday wasn't the first time Guerendo had the opportunity to extend playing time, but it was certainly his best performance. He rushed for 85 yards on 14 carries and scored his first career touchdown. He also gained 85 yards with a long run of just 19.

Head coach Kyle Shanahan told reporters after the game that the improvement for Guerendo was clear.

“I think he learned something from every run he made,” Shanahan said. “There were a few runs early in the year where he did quite well, but we rate him pretty harshly, all pretty harshly.” And he had a few, like four-yard runs, that we thought he could have gotten seven yards. We're pretty hard on him. And then you see how he translates that into training and everything that we really pushed him with, he was really coachable, he's not a sensitive guy, he's very detailed and he's very well prepared for a rookie. Things aren’t too big for him and he didn’t see much in the preseason, but after getting healthy there and over the course of this year, I feel like he’s gotten better every week.”

Guerendo also played a big role in the 49ers' Week 6 win over the Seattle Seahawks, but he struggled to find room in that game before a 76-yard run late in the fourth quarter helped the 49ers win. He finished the game with 10 carries for 99 yards.

On Sunday night, he was more consistent with runs of 19 and 15 yards on his first two touches. He showed off his pace and power and generally seemed more patient as he waited for running lanes to develop.

Shanahan also said Guerendo was doing so well that they didn't even try to get Mason back into the game after he came out in the second half with his helmet on – a sign that he was ready to play.

Guerendo rewarded the 49ers' faith in him by rushing for 47 yards and a touchdown on 11 carries in the second half. He also contributed as a pass catcher, catching three of his four targets for 17 yards.

Guerendo's talent has always been obvious, he just hasn't broken through like we've seen other RBs in Shanahan's scheme. Sunday night was his coming out party, and it came in a game where the 49ers desperately needed their running game to turn things around after a difficult first half.

With Christian McCaffrey set to return soon, Guerendo may not get another chance as the lead RB this season, but he took advantage of his chance on Sunday night and played well enough to be a key factor in a big 49ers win.

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This article originally appeared on Niners Wire: 49ers offense gets boost from unlikely source against Cowboys