There are certain rivalries that will undoubtedly last forever. Cardinals fans and Cubs fans will be traveling back and forth on I-55 to yell at each other for decades. Giants fans and Dodgers fans will never be best friends. There will be New England parents who will refuse to support their children marrying Yankees fans until the end of time. Some rivalries are eternal.

But other rivals pop up, organically, amidst intense competition, overt familiarity and just good old-fashioned spite. And why wouldn’t they? Everybody wants to win … and they’ve got that one team constantly standing in their way. These rivalries won’t last as long as the Red Sox-Yankees bile will, but in the moment, and over the course of a season, they’re just as fierce.

It’s something that comes to mind right now, in the midst of MLB Network celebrating Rivalry Week, which continues this weekend with broadcasts of three intradivision clashes: Dodgers-Padres (Friday, 9:30 p.m. ET), Yankees-Rays (Saturday, 4 p.m. ET) and Astros-Mariners (Saturday, 9:30 p.m. ET). Meanwhile, the Twins and Guardians also open their series Friday (7:10 p.m. ET) as part of the Apple TV+ doubleheader.

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Here’s a look at the biggest pop-up rivalry in each division today, with all four of those matchups making the list.

AL East: Yankees-Rays

It has been two years since FiveThirtyEight’s Neil Paine proclaimed that the Yankees and Rays were the real rivals in the AL East -- sorry, Red Sox, gotta win more games! -- and the rivalry has only gotten more fierce since then. Kevin Kiermaier may be in Toronto now, but the longtime Ray summed up why the Rays and Yankees are such perfect rivals last year:

“The Yankees, they’ve got the big payroll, the mega-superstars,” Kiermaier said. “And then you’ve got the Rays. The small payroll. Not a whole lot of household names, but a lot of above-average Major Leaguers. And guys who know how to win.”

That’s particularly true this year, with the Rays off to such a blistering start, and the Yankees one game above .500 … but still in last place. Add in the Yankees’ Spring Training facility being located in Tampa, and you’ve got the ideal 2023 rivalry.

AL Central: Guardians-Twins

The way the AL Central has shaken out over the last decade, these are essentially the only two teams who could be rivals. Since the Royals won the division (and the World Series) in 2015, this pair has won six of the seven division titles, with the Guardians winning four and the Twins two. With the division falling apart around them -- the Twins are three games up on the Guardians, and the Tigers are a distant third, five games back -- this may remain the case for a while.

One of the most fun things about rivalries is that they work best when the rivals are similar: We always hate most what most reminds us of ourselves. This is the Twins-Guardians rivalry in a nutshell.

AL West: Astros-Mariners

There is an alternate history out there in which this does not happen:

The Mariners, in their first postseason in 20 years, are one out away from taking home-field advantage from the hated, forever-lurking Astros: All they need to get is that very last out. And then Yordan Alvarez launches that homer into the throngs of screaming Houston fans, and at that point, the Astros were off, well on their way to their second World Series title. The Mariners, with all their young talent, believe their story is just beginning. But they, like everybody else, have to get past the Astros first.

NL East: Braves-Mets

All right, so this isn’t exactly a new rivalry. Chipper Jones does have a son named Shea, after all. But, with apologies to the Phillies (who, uh, did make the World Series last year), these two teams look loaded and ready to lock horns for the next half-decade.

The Braves have a core group that’s signed for years to come and looks very much primed to win another World Series at some point -- if not more. Meanwhile, the Mets are, suffice it to say, very motivated to do whatever it takes to take the NL East mantle from the Braves and win their first championship since 1986. To see how intense this one can get, look no further than the end of last season, with the Braves sweeping that series from the Mets and claiming the division for the fifth straight year. And they’re just getting started.

NL Central: Brewers-Cardinals

Now, if this is going to remain a rivalry, the Cardinals are probably going to have to get out of last place at some point. But assuming that happens, these two teams are going to tangle like they have essentially this entire century. The Cardinals’ success has been well-documented. But it’s worth remembering how many headaches they’ve provided the Brewers, from 2011 (one of the best Brewers teams ever that ultimately fell to those streaking Cardinals in the NLCS) to last year, when the Brewers vexed the Cardinals all season until the Josh Hader trade sent the team plummeting. One fun thing about this division rivalry: They’ve actually faced each other in the World Series before, in 1982. (The Cardinals won that one, too.)

NL West: Dodgers-Padres

This has to be the biggest one at the moment, right? The Padres have forever been in the shadow of their Southern California neighbors, but something seemed to switch when the Padres became the only major sports franchise left in San Diego, following the departure of the NFL’s Chargers. The Padres’ aggression in trying to take down the Dodgers has only ramped up, and they have beaten the Dodgers at their own game by bringing in every big name imaginable, from Manny Machado to Juan Soto to Xander Bogaerts. It hasn’t worked in the regular season yet, but during last year’s NLDS, the Padres finally broke through. These two are going to be punching each other in the throat for years to come. We’re all just lucky enough to get to watch.