The Lamar Hunt U.S. Open Cup might be the hidden gem of American soccer, underappreciated and undervalued. But the beauty and unpredictability that is the Open Cup might not stay tucked away much longer, given the increasing exposure the tournament is receiving.

The tournament is the second-oldest continuously operating club competition in the world after the famed FA Cup, and while the American version is clearly dwarfed in prestige and media coverage by its English counterpart, the Open Cup is not without its wonder and shocking twists.

Upsets abound, and clubs can put themselves on the map with a strong showing in the competition. Playing in small, sometimes rundown venues in obscure cities is all part of the mystique that is the Open Cup. Catch the fourth round of the competition on ESPN+ starting at 7 p.m. ET Tuesday.

More than a game

The beauty of the Open Cup is giving smaller clubs the opportunity and platform to play against bigger teams from more prominent leagues. Very often when a lower division side hosts an early round Open Cup fixture, it is more than a game.

Atmospheres can be intense, and conditions very likely are different and inferior to what MLS teams are used to. Locker rooms can be spartan, fields can be patchy and worn, and getting to the venue can be a challenge. Sometimes leaving can be even worse, as was the case for the New York Red Bulls in a 2012 Open Cup third-round match.

Coming off a 3-0 win at the Charleston Battery, the Red Bulls' charter flight from South Carolina was canceled due to a storm. The team needed to get back to New Jersey to begin preparation for the fourth round at Harrisburg City.

"A hurricane was coming, so planes were grounded, and we had to take buses all the way back," defender Heath Pearce told ESPN FC.

At the airport, team administrators had to scramble and rented two midsize buses for the team to pile into. During the dead of night, the Red Bulls drove nearly 12 hours to get back to what was then their training center at Montclair State University in New Jersey.

The next week, there were no travel gaffes, but the Red Bulls, with the same Starting XI as the week before, lost in extra time at Harrisburg. Such is the Open Cup.

Big club most likely to not advance

Let's call it like it is: New York City FC have not traditionally fared well in this tournament. In fact, it isn't much of a priority for this club, with NYCFC having never won a game since debuting at the tournament in 2015.

This year's opening round will tax the team's depth, given recent international call-ups. The good news is that, despite the roster restrictions of the tournament, NYCFC have a relatively deep team. That said, this is likely going to be a very young squad going up against a motivated USL team in North Carolina FC (7 p.m. ET Wednesday on ESPN+).

"Right now, we have just for the Open Cup, 14 players and two goalkeepers," NYCFC head coach Domenec Torrent said when asked by ESPN FC about prioritizing the Open Cup.

"It is not easy, but we'll try to do the best team possible to play and to try to win the first game. But most important thing for me in the Open Cup is trying to play with the players who need minutes."

Across four games in their Open Cup history, NYCFC have managed just two goals.

Team most likely to take this very seriously

Five times in the past seven years, the Philadelphia Union have made at least the quarterfinals of the Open Cup. Four times in that stretch they made the semifinals, and thrice they were finalists.

Although they've never won the tournament, this is an organization that has taken the Open Cup seriously. Last year, their run to the final of the competition helped propel a return to the playoffs for just the third time in franchise history.

Head coach Jim Curtin, who won the Open Cup in 2003 and 2006 as a player with the Chicago Fire, said the Union will go after their fourth-round match at D.C. United (7 p.m. ET Wednesday on ESPN+) with a "strong group of experienced players" mixed in with some squad rotation.

"Look, there are only two trophies our country has -- the U.S. Open Cup and MLS Cup -- and we're going to continue to go after it. Obviously, we've fallen short three times, and as hard as that has been for us and our fanbase, it is still a goal of ours," Curtin told ESPN FC.

"We'll put a squad on the field that can go to D.C. to get a result and get a win, to survive and advance in the tournament. We'll always treat it with the respect that it deserves. It has been instilled in me since my Chicago Fire days that it is an important trophy, one that we'll go after with the Philadelphia Union again this year."

Last season the Houston Dynamo defeated the Philadelphia Union 3-0 to win their first U.S. Open Cup title. Photo by Bob Levey/Getty Images

The headliner

The biggest matchup of this fourth round is intriguing not just because it is two MLS clubs against each other but also because it is arguably the best rivalry in the country.

Seattle Sounders vs. Portland Timbers (10:30 p.m. ET Wednesday on ESPN+) is simply a fun and exciting prospect because of the derby atmosphere around these two teams. It is also downright predictable.

This week's match is the fourth time in the past six years that these two Cascadia Cup rivals will have played each other in the tournament. Predictable? Yes. Boring? Certainly not.

The Sounders have historically owned their Open Cup meetings with the Timbers and are undoubtedly kings of the tournament.

Four times since 2009 they've lifted the Cup. Another win would see them tie the Bethlehem Steel and Maccabi Los Angeles for the most Open Cup titles of all time.

Upset alert

Much like the FA Cup, upsets happen all the time in the Open Cup.

Two years ago, amateur club Christos FC, based out of a liquor store in Baltimore, Maryland, almost beat D.C. United in the fourth round. In 2012, amateur side Cal FC, coached by former United States international Eric Wynalda, beat the Portland Timbers.

The makeup of an upset is simple, Wynalda told ESPN FC.

"The Open Cup doesn't always get maximum effort from all the clubs that don't make it a priority," Wynalda said. "The bottom line is that the teams that give it the energy it requires will get the most out of it. Depth is the key to make a long run in the competition."

Although there isn't a Christos or a Cal left in the tournament this go-around, perhaps a team such as Memphis 901, featuring a number of MLS players on loan in the USL, could provide an upset. Especially with a favorable matchup against Orlando City (8:30 p.m. ET Wednesday on ESPN+), who have struggled in MLS this year and don't feature a ton of depth. Fellow USL side New Mexico United could also be a tough out, as in just their second season, the club sits in first place in the USL's Western Conference and draw a Colorado Rapids side that that has the third-fewest points in MLS so far this season. (9:00 p.m. ET Wednesday on ESPN+).

One other matchup to watch is minnows Orange County FC at the LA Galaxy (10:30 p.m. ET Wednesday on ESPN+). OCFC are the lowest level team left in the field, playing in the fourth tier National Premier Soccer League, and are coached by former Galaxy player and U.S. Soccer hero Paul Caligiuri. Orange County will have a tall task on their hands with the Galaxy, but then again, this is the Open Cup.

Wasn't always a big deal

The tournament has a long ways to go to be accepted by American soccer fans, let alone go mainstream, but the Open Cup has grown by leaps and bounds in recent years. MLS clubs' playing in the tournament has gone a long way toward increased visibility for the tournament.

But first-division sides rarely participated in the tournament, with NASL clubs from yesteryear turning their noses up at the Open Cup and rarely if ever participating.

"The Open Cup at the time, despite what revisionist history likes to romanticize ... wasn't on anyone's radar screen," former NASL goalkeeper and current MSG broadcaster Shep Messing told ESPN FC. "It was more of a tournament for leagues like the German American League and teams like [New York] Hota [Bavarians], the [United] German-Hungarians, etc. Even in the early days of NASL ... before Pele ... there was never a thought given to the U.S. Open Cup."

It wasn't just the NASL

In its inaugural season in 1996, only four MLS sides entered the Open Cup. Eventual champions D.C. United were among those four entrants from the league, winning the Open Cup to complete their domestic double. The reason for the low turnout from MLS teams, according to then-MLS commissioner Doug Logan, was simple.

"I believe the 'party line' was that we had our hands full with our own competitions that first year," Logan told ESPN FC. "If truth be told, there was probably some anxiety that some of our teams would get their asses kicked by well-coached, lower division teams. I remember the first year we [entirely] competed going to Rochester and watching the Lancers run the [Tampa Bay] Mutiny and its slow back line right out of the stadium."

Logan might have been on to something. In 1999, the Rochester Raging Rhinos of the now defunct A-League won the Open Cup, defeating four MLS sides on their way to lifting the trophy.