Landon Donovan - LA Galaxy - waves on return from retirement vs. Orlando City

With the three other lower-seeded teams still in with a shot at joining the Portland Timbers and springing a Conference Semifinal surprise in 2018, it felt like a good time to look back over league history to find the biggest playoff upsets that took place after any preliminary rounds but prior to MLS Cup.

It really should come as no surprise that the all of our picks here occurred in the Conference Semifinals, as that round is more likely to pit two teams far apart in the regular-season standings against each other.

Before we get started with the ranking, let's pour one out for the nearest miss: The Montreal Impact's surprise Eastern Conference Semifinal disposal of the New York Red Bulls in 2016.

No. 5: New England over Columbus Crew SC, 2004

The top 5 conference series upsets in MLS Cup Playoffs history -

New England's Taylor Twellman | Getty Images

The New England Revolution finished an underachieving regular season 16 points back of Supporters’ Shield victors Columbus, and needed a closing-day win over Chicago just to edge out the Fire for the last playoff spot on goal differential.

Nevertheless, Steve Nicol had a strong side that featured Rookie of the Year Clint Dempsey, Shalrie Joseph, Pat Noonan, Steve Ralston and Taylor Twellman. Those players all showed up for the Conference Semifinals, which opened with the underdogs claiming a 1-0 home triumph on Avery John's first-half strike.

Columbus turned up the heat in the decisive second leg at Crew Stadium (now MAPFRE Stadium), but squandered a host of early chances. Their profligacy grew as the match wore on, with both Ross Paule (a perfect 4-for-4 from the spot during the regular season) and Tony Sanneh having weak penalty-kick efforts denied by Revolution backstop Matt Reis.

Twellman then doubled the Revs' aggregate lead nine minutes from time, rendering a stoppage-time goal by Edson Buddle as mere consolation.

No. 4: New York Red Bulls over Houston Dynamo, 2008

The Red Bulls squeaked into the postseason by a single point, and their reward was being shipped over to the West bracket to face two-time defending league champs and 2008 Shield runners-up Houston in the Conference Semifinals.

Few observers gave the Red Bulls a chance against a team that had outdone them by 12 points during the regular season. But they drew first blood when Juan Pablo Angel nodded home shortly after intermission of a physical Giants Stadium leg. The Dynamo responding by piling on the pressure until Kei Kamara stabbed in a loose ball five minutes from time to seemingly put the MLS Cup holders back in control.

However, that notion was thrown out the window when Dane Richards surged up the middle to put RBNY ahead to stay midway through the opening frame of the return. Ten minutes later, the Jamaican winger got loose on the right and his cross was blocked by Ricardo Clark's arm, setting up Angel at the spot to double the aggregate lead.

Houston threw everything they could at away goalkeeper Danny Cepero, to no avail. Nine minutes from time, Richards broke free down the right again, centering for John Wolyniec to snap his 28-game goal drought by hammering in the final nail. The Red Bulls went on see their improbable run end with an MLS Cup defeat against Columbus.

No. 3: Chicago over D.C. United, 2007

The top 5 conference series upsets in MLS Cup Playoffs history -

Chris Rolfe with Chicago | Brian Kersey/Chicago Fire

D.C. United were fresh off winning a second straight Supporters’ Shield with an experienced, cohesive squad with several key cogs still around from their 2004 MLS Cup title team. On the other hand, the exciting but highly inconsistent Fire had the fewest wins and the second-worst goal differential out of the eight-team playoff field.

Just 14 minutes into the Toyota Park opener, Chicago showed they were ready to rumble with a capital crew that had outdone them by 15 points in the regular season. The Black-and-Red defense misjudged a long bouncing ball and Chris Rolfe swept in to fire the first leg's only goal.

The upset was well and truly on when the Fire scored two goals late in the first half of the return leg at RFK Stadium. Chad Barrett and Rolfe struck two minutes apart, each set up by’s own Calen Carr, to put Chicago in the series’ driver seat. Clyde Simms and Christian Gomez hit late to pull D.C. within one, but that is where the home side's deciding-leg rally stalled.

No. 2: Real Salt Lake over Columbus, 2009

When the 2009 MLS Playoffs began, Real Salt Lake had played all of one postseason match in their short history, and that game ended in a tough Conference Championship home loss to that same Red Bulls side the year prior. Finishing nine points behind Shield-winning MLS Cup champions Columbus, they narrowly made it back to the postseason on the head-to-head tiebreaker after ending the regular season level on points with both Colorado and D.C. United.

It may not have sounded like the starting point of a title run at the time, but RSL quickly showed they meant business against a stacked Crew SC side led by Guillermo Barros Schelotto. They kept an insistent Columbus attack off the board until Robbie Findley tucked a Yura Movsisyan cross past Will Hesmer in the 88th minute of the opener at the RioT.

Though RSL were ahead to start the away leg, Columbus had to like their chances of flipping the scoreline at home. They liked their chances even better when Barros Schelotto bagged a brace in the opening 35 minutes to put the champs on top in the tie.

The feeling didn't last long. Less than two minutes later, Javier Morales scored to pull RSL level (the away goals tiebreaker was not used at the time). Just before the break, Frankie Hejduk hauled down free-kick target Fabian Espindola to concede Columbus' first penalty of the entire season and Robbie Findley converted to put the underdogs on top. Andy Williams completed the upset sweep with an angled, seeing-eye strike in the 74th minute.

No. 1: LA Galaxy over San Jose Earthquakes, 2005

After a solid 2004 regular season that ended in playoff failure, the LA Galaxy turned over nearly two-thirds of their roster heading into the following campaign. One of those new players was US men's national team star Landon Donovan, who was making a Cali Clasico switch (via Bayer Leverkusen) after helping the Earthquakes claim two MLS Cups in four seasons.

Even with that talent swing, the 2005 Quakes were Supporters’ Shield winners coming off one of the best MLS seasons at the time. They had a host of guys with two titles already under their belts that would soon go on to win back-back to crowns in Houston, plus Danny Califf and Mark Chung. They ended the regular season 19 points above the rival Galaxy, who backed into the playoffs on a tiebreaker after dropping a 3-1 home decision to their derby rivals on closing day.

It had been a roller-coaster campaign for LA, who were hindered throughout the summer and fall by national team call-ups and their run to the U.S. Open Cup crown. They got their act together in time for the first leg, which saw them exact fast revenge with a 3-1 home victory over San Jose. Donovan's 39th-minute tally stood up as the winner, and he also skillfully added late insurance to put his former side in a bind.

In the second leg at Spartan Stadium, Brian Ching gave the Earthquakes hope by slicing the aggregate lead to one a moment before halftime. The comeback was cut short, however, as Ned Grabavoy restored the visitors’ two-goal advantage and the Galaxy were on their way to a second MLS Cup title.