Jordan Mason's 147-yard night helps the 49ers win Monday night without Christian McCaffrey

Mason carried the ball an incredible 28 times for 147 yards and scored a 5-yard touchdown in the third quarter that increased San Francisco's lead to 23-7. According to NFL Research, his 28 carries were the most of any running back in Kyle Shanahan's time as head coach of the 49ers.

“When you pass him the ball, he breaks tackles and usually gets more than we block,” Shanahan said of Mason. “When he had the good lanes, he always hit them and got a lot, but JP was fantastic today.”

With his strength and agility, Mason was the catalyst for a Niners attack that overcame a 7-3 first-quarter deficit with 23 straight points from five consecutive drives to put the game out of reach.

The only thing that seemed to rattle Mason was a postgame interview with ESPN's Lisa Salters.

When Salters asked when he found out when he would start, Mason said Friday:

“When did I find out? Maybe Friday, Friday night, something like that?” Mason said. “I was always prepared, I mean, we went through training camp, I was RB1 in training camp, so I prepared from then on.”

Friday was the day before McCaffrey was listed as questionable.

Shanahan later told the media that he never mentioned to Mason that he was in the starting lineup, but stressed that he would be used to a much greater extent than before.

“I never told Jordan he was going to start,” Shanahan said. “I told him he had to prepare a lot, but maybe it was (running backs coach) Bobby (Turner) or somebody trying to get him pumped up. But I knew he had to play a lot, I told him he had to, it's not going to be like usual, it's going to be a No. 2 running back splitting most of the time, but no, he didn't know until today that he was going to do that for sure.”

By the time it was Mason's turn to take the podium, the shine of his great game had clearly faded.

“That exact question is why I'm angry, that's why I don't like talking to the media because you say something wrong and then you know,” Mason said when asked to clarify his statement again when told when he started. “I don't know, just skip that question.”

Regardless of when he was informed, Mason got the 49ers going on their first touchdown run. He carried the ball four times in a row, making 5, 6, 9 and 18 yards before the latter was backed off by a holding call. Two plays later, Mason ran around right end for a 17-yard touchdown that was also nullified by a holding call. Nonetheless, he had set a punishing tone that the Jets could not withstand.

Shanahan said McCaffrey, who missed every preseason game and training camp before returning last week, hasn't had a setback with his calf/Achilles injury, but his calf was too much trouble for him to play on Monday. The problem comes and goes, Shanahan added.

If CMC's woes continue to be a problem, the 49ers know they have a solution in Mason.

Mason, an undrafted free agent from Georgia Tech, made his first career start Monday night. Before the game, the 25-year-old had career highs of 11 carries as a rookie in 2022 and 69 rushing yards last year in a blowout of the Dallas Cowboys. He has more than doubled those numbers.

Before Monday night, Mason was the RB1, but earlier this season he was actually the RB3 behind McCaffrey and Elijah Mitchell. Mitchell is out for the rest of the season.

How much Mason will play this season will likely depend on CMC's health, but Mason is confident he can handle the physical demands of being a starter and getting the reps and playing time he needs.

“Everything is fine,” Mason said of his physical condition. “It's just the beginning.”

Shanahan has found another running back who can further bolster his offense, and even if it was just for one game, Mason had a really great Monday in the 49ers' season opener.