Change moves fast in MLS these days. So fast, in fact, that a quick glance back at even relatively recent seasons' past can often reveal a very different-looking league, one with a few unrecognizable characters and others strangely altered, as if their current identities were projected through a fun-house-mirror effect.

Tuesday's US Open Cup final between Real Salt Lake and D.C. United (9 pm ET, GolTV) offers a particularly jarring example.

The last time D.C. United won a championship final was 2008, when they defeated the Charleston Battery 2-0 at RFK Stadium to claim that year's Open Cup title.

It was their 12th trophy in 13 years of existence – and actually something of a consolation prize for an ambitious club which had expensively rebuilt a Supporters' Shield-winning team in the hopes of winning both domestic and international competitions, only to crash out of CONCACAF play and miss out on the MLS postseason.

Five years later, United have lost their flagship status and “We Win Trophies,” the chest-beating slogan of their unsuccessful 2009 USOC defense, and has taken on a harsh edge in retrospect as the ensuing five years brought a four-year playoff drought, a club-worst season in 2010 and a conspicuous absence of hardware. (For those interested, the wewintrophies.com domain name appears to be available for sale at the moment.)

Over the same period out in Utah, a few familiar faces have helped turn an expansion laughingstock called Real Salt Lake into one of MLS' most dependable contenders, building, from the ground up, a finely tuned success machine that very much resembles what United once were.

That was the first full year in charge for senior vice president and GM Garth Lagerwey and head coach Jason Kreis; that fall, RSL made the playoffs for the first time in club history, and have done so in every season since.

“The Team is the Star” at Rio Tinto Stadium, and style and ambitions do not change even when the faces do. United alums Lagerwey and Nick Rimando and Maryland native Kyle Beckerman – who'd probably be wearing D.C. colors had the MLS Homegrown program come into existence a decade ahead of schedule – are three who have stuck around, becoming some of the most influential figures in a half-decade of strong, steady growth.

Now these clubs meet in the decisive match of the 100th anniversary edition of the nation's oldest cup competition. Their reversals of fortune are reflected all too accurately in the current league standings, as RSL sit one point off the pace in the Supporters' Shield race and United languish in last place. Both hunger for the cup, but do so with widely differing palates.

For weeks, Tuesday's match has been the last remaining game of real consequence in a tough season for D.C., a chance to win a title for the first time since '08 and give their players and supporters something to cheer in a year that is, in some statistical contexts, even worse than the 2010 campaign that still provokes shudders in those who experienced it firsthand.

Black-and-Red fans have facetiously talked of “pulling a Wigan,” taking inspiration from the English club which won that nation's famous FA Cup last year even as they slid into relegation to the second division with an 18th-place league finish.

For Salt Lake, it's an opportunity to mark their sustained excellence with something tangible, to end their own drought in the quest for a second trophy to add to the 2009 MLS Cup. It's also an express ticket back to the CONCACAF Champions League, the tournament which has brought some of their history's highest and lowest points since 2010.

“We said for the next six weeks that the most important match for us is the Open Cup final,” said Kreis over the weekend. “And yes, we want to compete for the Supporters' Shield, but for me, the chance to win something in a one-off game has to take precedence. We are also very excited for the opportunity that we have, and really excited to play that matchup in front of our fans.”

There's little doubt that the awarding of a CCL place to the winner – another new wrinkle also dating back to 2008 – has transformed the Open Cup, at least in the minds of MLS clubs previously prone to using it as a de facto reserve league game.

With wave after wave of challengers crashing on its rocks over the years, the CCL remains the white whale of MLS, with mere participation a source of pride and, for some, an agenda-setting priority in its own right. In this case, it would also provide both Kreis and his opposite number Ben Olsen with a valuable carrot in their offseason pitch to new recruits, and an extra brass ring for everyone at their clubs to hunt.

It's not often that MLS teams rest their regulars in league play to prepare for an Open Cup game, but that was exactly what unfolded on Saturday, as a reserve-laden RSL squad defeated the Vancouver Whitecaps 1-0 and United's backups fell 4-1 to Toronto FC. In both cases, several key starters didn't even make the trip, with Tuesday's final taking precedence.

“Obviously our whole season comes down to 90 minutes against Salt Lake,” said Jared Jeffrey, D.C.'s goalscorer on Saturday. “It's been a trying year, but we have an opportunity to salvage something on Tuesday and we're really looking forward to it.”

Separated by 36 points in the standings and 11 objects in the trophy case, United and RSL have different reasons for lusting after the Dewar Cup, the trophy awarded to the Open Cup champs – and both would be wracked by similar amounts of soul-searching should Tuesday's clash unfold adversely.

After all, both clubs remember all too well how the other half lives.