Sandy Koufax vs. Bob Gibson. Tom Seaver vs. Steve Carlton. Roger Clemens vs. Pedro Martinez. Stretching all the way back to the turn of the 20th century, when Christy Mathewson squared off against Mordecai “Three-Finger” Brown, few things in baseball are as exciting as a duel between two premier aces.

For the 2020s, that matchup very well could be Dodgers wunderkind Walker Buehler against Cardinals star Jack Flaherty. The two former first-round Draft picks are almost unquestionably the National League’s most promising pair of young pitchers (they were all over MLB.com's expert picks for The Vault), and even if this year’s unusual circumstances might rob us of their head-to-head matchups, we should see them square off for two of the NL’s most prominent clubs for years. Buehler and Flaherty have crossed paths twice so far -- both times in late summer 2018 -- and combined for two runs allowed across 27 combined innings.

These two studs debuted within six days of each other in September 2017 and, aside from a handful more games pitched by Flaherty, their outstanding numbers almost mirror one another:

Buehler: 62 G (53 GS), 329 IP, 3.12 ERA, 1.04 WHIP, 28.6% strikeout rate, 7.9 fWAR
Flaherty: 67 G (66 GS), 368 2/3 IP, 3.20 ERA, 1.06 WHIP, 29.2% strikeout rate, 7.0 fWAR

That was the past, but we’re looking toward the future. Here’s what we can expect from these two stars.

Future projections: Strong (like, really strong)

While we’re waiting for actual baseball to come back, the on-paper projections for Buehler and Flaherty, beginning with FanGraphs and ESPN contributor Dan Szymborski’s ZiPS system, are downright tantalizing. Buehler’s No. 1 comparable heading into this year? None other than Seaver. And for Flaherty? That would be Clemens, that guy who won seven Cy Young Awards. Umm … sign us up for all of that.

ZiPS is also kind enough to let us dream further with its set of three-year projections, and, once again, the future is sterling for both aces -- with a slight edge given to St. Louis’ righty (keep in mind that the 2020 projection has not been shortened to account for the coronavirus pandemic, so there’s a teaspoon of fantasy involved here):

Buehler (next 3 seasons): 86 GS, 500 IP, 3.20 ERA, 1.06 WHIP, 10.9 K/9, 12.4 WAR
Flaherty (next 3 seasons): 100 GS, 570 IP, 3.06 ERA, 1.04 WHIP, 11.2 K/9, 14.9 WAR

Declaring these two careers a wash to this point is an easy call. The much harder part is picking the better pitcher going forward. Here’s each ace’s best case:

The case for Buehler

Flaherty’s edge in those projections above might surprise some, given that Buehler and his blazing arsenal have claimed the lion’s share of hype. The Vanderbilt alum likely might have contended for the No. 1 overall slot in the 2015 MLB Draft had he not injured his elbow, and he was MLB Pipeline’s second-ranked right-handed pitching prospect behind Michael Kopech when he debuted two years later. It wasn’t hard to look at Buehler and immediately label him as Clayton Kershaw’s successor in Los Angeles.

Buehler’s promise has always revolved around his overpowering four-seam and two-seam fastball combination that averaged 96.5 mph last year (fifth highest among full-time starters). With that heat tied to a plus curveball and a slider-cutter hybrid, Buehler has one of the most advanced repertoires in baseball, regardless of age, and it all clicked into place when he posted a 2.62 ERA in the 2018 regular season. By the time Buehler roared off the mound following seven scoreless innings in Game 3 of that year’s World Series -- to the standing ovation of Koufax -- his potential had shifted into sixth gear. Buehler is not only supremely talented, but he also seems to raise his level for the biggest games.

Last year didn’t do anything to dampen expectations, as Buehler enjoyed his first 30-start campaign and put up an absurd 215-to-37 strikeout-to-walk ratio. He punched out nearly the same rate of hitters as Flaherty and issued fewer free passes. And while Flaherty’s second half for the ages pushed his ERA down to a half-run lower than Buehler, L.A’s ace actually posted a slightly lower expected ERA (3.28 to 3.36) based on Statcast’s contact quality metrics.

Buehler can simply overpower a hitter, and a high-octane fastball can age pretty darn well -- just ask Justin Verlander, the pitcher whom Buehler eerily mimics on the mound. Plus, the Dodgers’ seemingly endless farm system and deep pockets (remember how they just acquired Mookie Betts?) probably have Buehler set up for plenty of primetime October starts in the future.

The case for Flaherty

Flaherty, who attended high school 20 miles from Dodger Stadium, doesn’t routinely challenge triple-digits like Buehler, but it might surprise you that he topped his L.A. counterpart in both strikeout rate and whiff-per-swing rate for two years running. His 94-95 mph fastball holds up just fine, but his true advantage lies with his breaking balls -- especially his slider. Batters hit just .185 and missed on roughly 45% of their swings last season against Flaherty’s signature offering, giving him an out pitch that might top anything in the dynamic Buehler’s bag.

Last year, Buehler came at hitters with his hard heat more than 50% of the time while Flaherty changed speeds a little more, and it was actually Flaherty who yielded less contact on hitters’ in-zone swings. That could be why ZiPS sees Flaherty piling up more a few more K’s in the coming years, and it also thinks he’ll give up fewer homers, translating to a slightly lower ERA projection.

As these pitchers age and their velocity tails off just a hair, Flaherty might have the head start when it comes to his secondary pitches. Plus, he's younger than Buehler by more than a year.

The tiebreaker?

Buehler has the explosiveness and Flaherty has shown a little more artistry, but the better outlook still doesn’t amount to much more than a coin flip. And so the biggest difference-maker could lie in the most unpredictable realm for any pitcher: his health.

Buehler’s elbow injury in 2015 necessitated Tommy John surgery, and, through a combination of caution by the Dodgers and a little more durability by Flaherty -- who has yet to go on the injured list in his young career, while Buehler suffered a microfracture in his rib in 2018 -- Buehler has taken the ball fewer times. Projection systems take prior injury luck into account, and that’s partly why ZiPS sees more WAR in Flaherty’s future, despite the two aces looking nearly identical in their rate stats. That could obviously flip in an instant, as the unfortunate reality is that Flaherty could develop elbow soreness just as quickly. And Buehler, it should be noted, didn’t miss a turn through the rotation last year.

In a perfect world, health never plays a role at all. The Dodgers and Cardinals are about as vintage an NL matchup as it gets, and here’s hoping that Buehler and Flaherty take the ball every time they clash.