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

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

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

Sunday wasn’t the first time Guerendo had the chance for extended 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 reached 85 yards on a long run of just 19.

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

“I think he’s learned from every run he’s made,” Shanahan said. “There are a few runs earlier this year where he did well, but we judge him quite harshly, everyone judges quite harshly. And he had a couple of four-yard runs where we thought he could have gone seven yards. We’re tackling him pretty hard. And then you see how he puts that into practice and everything that we really pushed him with. He is very coachable, he is not a sensitive guy, he is very detailed and he is very ready for a newcomer. Things aren’t too big for him and he hasn’t had much in the preseason, but once he got healthy there and throughout the 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 running room in that game before a 76-yard run late in the fourth quarter helped the 49ers seal the win. He finished the game with 10 carries for 99 yards.

He was more consistent on Sunday evening with runs of 19 and 15 yards on his first two touches. He showed off his speed and strength and generally looked more patient as he waited for the running lanes to develop.

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

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

The talent was always evident with Guerendo, but he just couldn’t catch on like we’ve seen other RBs do in Shanahan’s scheme. Sunday night was his coming out party and it came in a game where the 49ers desperately needed their run game to get going and help them turn things around after a rough first half.

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

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