Wait, what? The Cardinals have good young players, too?

Cardinals’ left fielder Randal Grichuk celebrates his walk-off hit to beat the Cubs 4-3 in Sunday’s season opener at Busch Stadium.

ST. LOUIS — One dramatic loss on Opening Night to the rival Cardinals on the road doesn’t figure to say much about the Cubs and their ability to defend their division and World Series championship over the next six months.

But the stifling start by the Cardinals’ Carlos Martinez and the two big late-inning hits by their left fielder, Randal Grichuk, was at least a reminder to the Cubs that they’re not the only team with the kind of 25-and-under talent that can do damage on a big stage.

And a reminder that the Cardinals might not be fading away from prominence as last year might have suggested.

Grichuk, 25, drilled a two-out, bases-loaded line drive to the base of the wall in left-center off Mike Montgomery for the walk-off game-winner in the Cardinals’ 4-3 victory.

The winner came one inning after Grichuk’s two-run homer to right off Pedro Strop extended the Cardinals’ lead to 3-0 and wiped out the Cubs’ mood swing delivered by Willson Contreras’ tying shot in the top of the ninth off Cards closer Seung-Hwan Oh.

Before the game, Cubs chairman Tom Ricketts focused on a young Cubs core that included five players, including Contreras, in Sunday’s lineup who were 25 or younger.

“If things play out like they can for players, they should improve over time,” he said. “It’s pretty exciting. It’s going to be a nucleus that stays together for several years and could be one of the most compelling teams in a generation.”

Ricketts won’t get a lot of arguments from most people around the game.

But the Cardinals had their own group of five who started who are age 26 or younger. And one of those was a starting pitcher younger than any in the Cubs’ rotation who might have the potential to be as good as any of them.

Martinez, making his first Opening Day start, put a stranglehold on the defending champs into the eighth inning, striking out 10, walking none and retiring 12 consecutive batters at one point and 18 of 19.

“Their pitcher was really good,” manager Joe Maddon said. “That was our issue tonight.”

“Impressive,” Cardinals manager Mike Matheny said of Martinez. “It was a big day for him, Opening Day, and he responded.”

Thanks to elder Cubs horse Jon Lester and young batterymate Contreras, the Cubs still had a chance to pick up in 2017 where they left off in November.

Lester battled traffic on the bases throughout his start but navigated around enough of it to hand off a 1-0 game to the bullpen in the sixth.

And even after Strop gave up the Grichuk homer, Contreras drove a low line drive off Oh into the left-field seats to stun the sold-out crowd at Busch Stadium.

“Great at-bat,” Maddon said. “The ball really did jump right there.”

The Cubs have 161 more of these to deal with before they can start thinking about the playoffs, including 18 more against the Cardinals.

“There’s a different air to this team,” Matheny said. “I’d say it’s a little bit of an edge, a little bit of a chip on our shoulder. The first day we walked into spring I sensed it.”

Maybe what happened Sunday night is nothing more than an example of what Cubs president Theo Epstein said was going to happen this year.

“This group is starting to know they have accomplished a lot together, and I think they feel good about themselves,” he said. “And I think they know the target’s on their back a little bit, that every time we come to play a series, teams are going to want to beat them.”

Lester, who has won three championships and pitched six openers, knows that much, possibly a factor in his ability to keep the game close despite giving up seven hits and two walks in his five-plus innings.

“This is Game 1 of 162, and we’ve got to find out our identity again this year, same as we had to last year and the year before,” said Anthony Rizzo, before going 1-for-4, including a fly to right that ended the eighth and left the bases loaded.

“Obviously, we want to win the division and get back there,” he said.

Follow me on Twitter @GDubCub.

Email: gwittenmyer@suntimes.com