SANTA CLARA — Mac Jones came to the 49ers to back up Brock Purdy after washing out in both New England and Jacksonville, working his hardest to be ready for called upon.

It happened sooner than anyone imagined when Purdy came out of a season-opening 17-13 win over Seattle with toe and left shoulder injuries which could sideline him for multiple games.

If that’s not enough to worry 49ers fans, Adrian Martinez will be promoted from the practice squad as the backup and he’s been with the team all of two weeks.

“It’s the front side of the season here, and I feel prepared,” Jones said Friday. “I’ve been working for this and fortunate to have started, I think this is my 50th game in the NFL, so I have my routine down, and I’m looking forward to the opportunity.”

Jones will start Sunday’s game in New Orleans against the Saints (10 a.m., PST, Fox). If there’s any concern about whether Jones is up to the task, it’s been well hidden. Teammates have lauded both his skill set and ability to quickly adapt to coach Kyle Shanahan’s system as well as his presence in the locker room.

After starting out leading the New England Patriots to a playoff berth to a rookie to being a backup for a poor Jacksonville team in his fourth season, Jones has plenty of experiences both good and bad to draw from.

“I’ve been fortunate to play in a lot of different roles, and your job as a quarterback is to either hand it off or throw it and that’s how simple I’m going to keep it,” Jones said. “That’s when I play my best, when I have a low pulse and just go out there and go through my reads and have that intensity and focus. You’ve got to be ready to play and have a system that works for you.”

Shanahan said he saw the same thing from Jones he’s seen every week since he signed a two-year, $7 million contract with the 49ers.

“It’s been awesome,” Shanahan said. “The same this week as he has been all camp. Our team really believes in him, our team really enjoys him and he did a hell of a job this week in practice.”

While Purdy’s persona is more laid back and serious, Jones by contrast is buoyant and quick with a joke among teammates.

“I definitely think that’s part of my personality, and I Play to have fun and try to win,” Jones said. “It’s hard when you’re in the NFL and it’s your job, but winning is fun, and I understand that. I want to go out there and be loose.”

Right tackle Colton McKivitz picked up on Jones’ penchant for being light-hearted immediately.

“That’s one cool thing about him, even in the huddle, he’ll still laugh and crack a joke, but when it’s game time, he locks in and commands the huddle,” McKivitz said. “He likes to have fun but he’s a winner. He’s proven that at Alabama and obviously now that we’ve got him, he’s going to want to show some stuff on Sunday. ”

General manager John Lynch believes Jones has fit in perfectly with the team and coaching staff.

Quarterback Mac Jones has won over teammates with his sense of humor as well as his ability to run the offense. Shae Hammond/Bay Area News Group

“What I can tell you is it’s probably better than advertised, better than what we thought he would be in terms of stepping in and just feeling like he was a real good fit for this offense,” Lynch said on KNBR-680.

Jones has already meshed with his teammates, and also has friendships on the roster from college (Brian Robinson Jr. played with him at Alabama), New England (wide receiver Kendrick Bourne) and Jacksonville (tight end Luke Farrell.

“I’ve know him since I was 17 years old,” Robinson said. “We were kind of in the same situation early in our career, second- and third-stringers. We weren’t playing much at the time. We had to work our way up to those spots and we constantly developed. I’ve watched his whole process all the way up to this point and have no doubt he’s ready for this opportunity.”

At Alabama, Jones passed for 4,500 yards, 41 touchdowns and four interceptions in leading the Crimson Tide to a national championship.

Selected with the No. 15 pick in the first round in 2021 in the same draft the 49ers traded up and took Trey Lance No. 3, Jones was named the starter by Bill Belichick and led the Patriots to a 10-7 record and a Wild Card playoff berth.

It turned out to be the peak of his New England experience, and one that Bourne saw up close after signing with New England in free agency.

“Mac helped me when I transitioned over there,” Bourne said. “It was his rookie year and I had one of my best years. But things go how they go. Every year is different. Some are good, some are bad. We both kind of fell victim to certain situations and things not going the way we planned. He kind of took it on the chin and just to see him here and the joy he has is great.”

Delighted to be in a place where he can “get back on track,” Jones found himself on the field the other day with both Bourne and quarterbacks coach Mick Lombardi, who was a New England assistant.

“Mick’s like, `Who would’ve thought we would all be be standing here on a Thursday afternoon — me, Kendrick and Mick,” Jones said. “Kind of crazy.”

Martinez, 25, played at Nebraska, Kansas State and most recently for the Birmingham Stallions of the UFL, winning the league Most Valuable Player award and leading his team to a championship.

If Martinez is nervous or intimidated at the thought of taking over should something happen to Jones, it’s not apparent.

“You come in, you learn the offense, you put in time, and I wouldn’t say it’s been any different than any of the other processes I’ve taken,” Martinez said. “I’m very confident. I think that’s part of my job, whether you’re a starter, second string or practice squad.”

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Martinez spent the Seattle game with an ear piece where he could hear communication between Shanahan and Purdy and learn the play-calling rhythm and game tempo.

Shanahan conceded he’d have to make some adjustments to his play-calling should Martinez be needed.

“He’s prepared for it all, but I’ll have an idea of the stuff he likes more than others,” Shanahan said. “I mean, he’s been here two weeks. You don’t tell a guy, `Hey, just take these 10 plays. You try to tell him to learn the whole game plan. But I always want to know what he’s more comfortable with and and hopefully we can stick with that if the game allows us to.”