Sam Darnold and Josh Allen often staged mini-competitions while working out together in the offseason, but the Jets quarterback knows Sunday’s season opener at MetLife Stadium against Allen’s Bills truly is “go time.”

The second-year signal callers first became friendly in the lead-up to the 2018 draft, with Darnold selected third overall and Allen tabbed by the AFC East rivals four picks later.

They already squared off once as rookies, with Darnold throwing for 170 yards and a touchdown in a 27-23 Jets victory in Orchard Park on Dec. 9. As divisional foes, it’s easy to envision Darnold and Allen starting against each other for years to come.

Darnold and Allen were ranked 31st and 32nd, respectively, among NFL quarterbacks in passer rating last season, and the potential return to contention for both teams — this year and in the future — is tied heavily to the maturation of their young franchise players.

“It’s going to be fun to go up against him the second go-around,” Darnold said after practice Thursday in Florham Park. “It’s fun to think about. Even on draft night, we talked about it a little bit, jokingly, but now that it’s actually here, it’s very serious.

“We’re both very competitive people.”

Indeed, Darnold said the two throwing partners competed in various drills “all the time” while training together in California. The Jets’ quarterback claimed to have come out on top in throwing accuracy, but concedes to his strong-armed counterpart on long-distance tosses.

“Yeah, that’s a given, he’s got me on that. He can throw it like 100 yards,” Darnold said. “He beats me at distance, and then some of the accuracy drills I got him.”

Allen initially backed up Bills starter Nathan Peterman last season, but the 6-foot-5 former Wyoming quarterback ended up starting 11 games, with 10 touchdowns with 12 interceptions, while running for another eight scores. He missed the other contest against the Jets with an elbow injury, with journeyman Matt Barkley fronting the Bills to a 41-10 blowout win at MetLife on Nov. 11.

Darnold, meanwhile, started in Week 1 as a rookie and 13 games overall, sitting out three games with a sprained right foot. He finished with 2,865 passing yards, 15 touchdown passes and 12 interceptions.

The former USC star also was impressive — 17-for-25 for 211 yards, with two TDs and no picks — in limited action in the first three preseason games this summer while learning a new offense under first-year head coach Adam Gase and offensive coordinator Dowell Loggains.

Darnold said he’s been talking “a ton” to Gase about which plays he feels comfortable running.

“I think I’m just in a different place now,” the 22-year-old Darnold said. “Being a rookie, going into my first game, I was feeling a little bit different. I wasn’t nearly as comfortable as I am now.

“I don’t think it’s because of the offense, necessarily. I love this offense that we’re in right now, but I just think it’s the comfort level with everything else. Given that it is Year 2, and knowing all the guys in the locker room. I think those are the reasons I feel more comfortable going into this Week 1.”

An Week 1 head-to-head pairing against Allen only adds to the ongoing competition between the two friends and budding divisional rivals.

“I think it makes it fun. It’s fun to kind of joke about it in the offseason and now that it’s here, it’s go time,” Darnold said. “Obviously, I’m going to talk to him after the game and all that, but we’re both really competitive.

“That first game everyone wants to get out there and play football. Especially with a new coaching staff, as players, we want to show what we’ve got. With new personnel, as well. We’re really excited. … Football is back and we’re ready to go.”