The U.S. Open Cup always seems to be a good source of storylines, and this year's semifinals certainly have plenty.

On one side, which we'll call the "West," there's Real Salt Lake and the Portland Timbers. Both are in the midst of competing for the Supporters' Shield, but are also seeking their first Open Cup titles.

On the other, which we'll call the "East," there's the Chicago Fire and D.C. United. Neither team is having a particularly good MLS campaign, but both have decorated pasts in the Open Cup. The Fire are attempting to tie the all-time record with a fifth title, as well as make it to a record-tying seventh final. United have won the championship twice and advanced to two other finals, but are also suffering through an absolutely horrid season.

Fire vs. United, Wednesday, 8:30 p.m. ET

The Fire got off to a rough start this year, starting 2-7-2. Coincidence or not, their season began to turn around at the same time they started the U.S. Open Cup on May 29. Since beating the Charlotte Eagles 2-0 in the third round of the tournament, they've gone 6-2-2 to move to within striking distance of the Eastern Conference playoffs.

As neat of a narrative as that makes, though, there are some personnel changes that have probably been a bigger part of the change. The biggest was the acquisition of hometown boy Mike Magee, who joined the Fire on May 24. Magee has scored eight goals and had two assists in 10 games, and is currently riding a three-match scoring streak.

Right around the same time, the Fire brought back defender Bakary Soumare. That has helped stabilize a defense that was sorely missing the veteran leadership of Arne Friedrich. With the two veterans leading the way, the Fire have moved to within five points of a playoff position after being virtually left for dead a few months ago.

The story hasn't been nearly as rosy for United, a team some thought were capable of making a run at the MLS Cup after they advanced to the Eastern Conference finals a year ago. Instead, they've been easily the most disappointing team of the season. At 13 points through 22 games, they are actually on a worse pace than they were during the disastrous 2010 campaign that was among the worst seasons in MLS history.

The Open Cup has been one of their only positives in a year that has featured a seven-game losing streak and a 13-match winless run. Until they beat the Montreal Impact last week, United had actually beaten as many MLS teams in their three Open Cup games as they had during their first 21 league matches.

Real Salt Lake vs. Portland Timbers, 9:30 p.m. ET

If this were a Western Conference final matchup, no one would be complaining. That it comes in the Open Cup semifinals is almost a disappointment. Both of these teams are enjoying wonderful seasons, with RSL leading the Supporters' Shield race and the Timbers just three points behind.

The Timbers have cooled off a bit since their 15-match unbeaten run ended on July 7, and have now won just one of their past five. But they still have just three losses all season and have the second-best goal-differential to, you guessed it, RSL.

More from our team blogs: RSL Soapbox Stumptown Footy

The Timbers continue to be this year's breakout team, as they are poised to make the playoffs for the first time since joining the MLS in 2011. Designated Player Diego Valeri's transfer was just completed on Tuesday, and they boast an attack that features five players with at least four goals. Valeri also has eight assists, which is the second highest total in the MLS this season.

RSL has actually cooled off a bit too. After winning 8-of-11 matches at one point, they have not won in their past three matches. They also have an explosive and varied offensive attack, leading the league with 37 goals and boasting five players with at least five goals. Also, like Portland, the main man in their attack is a central midfielder, with Javier Morales looking like his old self again by posting a solid five-goal, seven-assist season in just 19 appearances.

RSL has been outspoken about making the Open Cup a top priority over the past few seasons, but until now had little to show for it. Their three wins in this year's tournament are actually one more than they had during their first eight years of existence, as they failed to even qualify from 2007-10.

The Timbers' Open Cup history, while not as long, was similarly poor. The Timbers failed to qualify for the main draw in 2011 and lost their first match in last year's tournament. Dating back to their days in the USL, this marks the first time in the franchise's history that the Timbers have won more than two games in a single tournament.

Follow @SBNationSoccer on Twitter | Like SB Nation Soccer on Facebook

More in Soccer:

• Pressure starts to build on Clint Dempsey

• Juan Agudelo off to Stoke City

• LA Galaxy strengthen in goal

• Transfer rumours from SB Nation and our team blogs

• Full coverage of the NWSL