So much for the Panthers not being able to keep both their tailbacks.

Less than two hours before Saturday’s exhibition opener against Houston – and about a year after backfield partner DeAngelo Williams re-upped with a big contract – the Panthers’ Jonathan Stewart signed a five-year contract extension worth $36.5 million, including $22.5 million in guaranteed money.

The Panthers locked up the 25-year-old Stewart before he was eligible for free agency at the end of the season. Combined with the extension given to Williams, the other half of the so-called “Double Trouble” tandem, the Panthers have $43.5 million in guaranteed money committed to their two tailbacks.

Williams, 29, and Stewart, are among the six highest-paid backs in the league. Panthers general manager Marty Hurney said Stewart is too big a piece of the Panthers’ offense to let walk.

“There aren’t a lot of places that have two highly-paid running backs,” Hurney said. “First of all, I think good organizations keep their difference-makers. And he’s a difference-maker for us. And we’ve proven that both of them can share the load and have a dynamic impact for us.

“Those two guys get along great. DeAngelo’s as happy as anybody. And sharing carries helps keep those guys from the wear and tear and the pounding that running backs take.”

Stewart’s desire to be part of an organization on the rise outweighed any thoughts of going elsewhere as a team’s featured back.

“The Panthers got lucky and got a group of guys that understand the team aspect of winning football games. That’s ultimately what I want to do. I want to be on a good team, and this is a good team,” Stewart said. “And we’ve got a lot of good guys. The offensive line – Ryan Kalil, Jordan Gross – just all over the team we’ve got a lot of good guys. There’s no other place where I would want to be.”

Ben Dogra, Stewart’s agent, said the deal could be worth as much as $42.5 million. The contract is structured as a four-year contract with a club option for a fifth year.

Stewart received a $9 million signing bonus, and there is a $9 million option bonus the Panthers can exercise in the spring of 2014, Dogra said. The deal was designed to minimize the impact on the team’s salary cap, according to Dogra.

There was speculation last summer the Panthers would have trouble keeping both Williams and Stewart. That talk increased in March when the Panthers signed free-agent fullback Mike Tolbert, viewed as insurance if they were unable to re-sign Stewart.

Dogra said discussions about an extension for Stewart began after last season. They were finalized about 90 minutes before kickoff against the Texans.

“Talks have been going on for quite a while. We all thought it was best to keep it under the radar,” Dogra said. “Jonathan loves being a Carolina Panther and wanted to explore the possibility he could stay there the rest of his career.”

Stewart, a first-round draft pick in 2008, has rushed for 3,500 yards and a 4.8 yards-per-carry average. He and Williams became the first tandem in league history to rush for 1,100 yards apiece in 2009.

Stewart is the second-leading rusher in team history behind Williams, who is signed through 2015.

Since 2008, Stewart’s rookie year, the Panthers have rushed for 9,189 yards, most in the NFL. Besides his rushing numbers, Hurney said Stewart is valuable in the passing game and brings a toughness to the offense.

“I think everybody in that locker room is thrilled that he’s not going to leave at the end of the year,” Hurney said.

Stewart said Williams and several other players stopped by his locker before the game to congratulate him.

“We were happy,” quarterback Cam Newton said. “As a team you want to keep your core guys, and obviously Jonathan is a guy we feel we have to invest in, not only off the field but on the field.”

Hurney reiterated the team’s philosophy is to build through the draft and keep its key players, rather than spend big in free agency.

“This is a deal you want people to remember in March when everybody’s saying, ’Why don’t you get in on free agents?’” Hurney said.