Since joining Major League Soccer in 2010, there are four teams that Philadelphia has yet to beat: Real Salt Lake, FC Dallas, Portland, and weekend opponent Colorado.
The Union are 0-3-2 against the Rapids in five total tries, with back-to-back home losses in the last two meetings.
In 2010 and 2011, Philadelphia and Colorado played twice per year in the original "home and away" format. But in 2012, MLS debuted its "unbalanced" schedule, meaning that the Union would only play each Western Conference team one time per season.
Since the Rapids traveled to PPL Park in 2012, the Union head to Dick's Sporting Goods Park in 2013.
Here's a look at the brief history between the two clubs.
1. August 14, 2010 Philadelphia 1, Colorado 1 (PPL Park)
Goals: Larentowicz 59', Mwanga 73'
Danny Mwanga scored his second goal in as many weeks to earn the Union a 1-1 draw in their first ever game against the Rapids.
The Union controlled most of the game, with Alejandro Moreno hitting the post before two disallowed goals and a penalty claim that wasn't granted. The Rapids capitalized on the opportunity to take a 1-0 lead through Chestnut Hill Academy alumnus Jeff Larentowicz.
Mwanga's 73rd minute equalizer was his seventh goal of the 2010 season.
2. Sept. 29, 2010 Colorado 4, Philadelphia 1 (Dick's Sporting Goods Park)
Goals: Cummings 8', 15', Thompson 68', Amarikwa 86', McInerney 90+
One of the more forgettable games in Union history, Colorado rolled to a 4-1 victory.
Philadelphia entered the game with a 3-1-1 record over the prior five matches.
But Omar Cummings bagged a first half brace, with Wells Thompson and Quincy Amarikwa tallying in the second half.
The silver lining was a stoppage time strike from Jack McInerney that earned a goal of the week nomination.
3. June 4, 2011 Philadelphia 1, Colorado 1 (Dick's Sporting Goods Park)
Goals: Casey 63', Mwanga 66'
Philadelphia came into this game on a two game winning streak, the Zolo offense finally coming to life in a 6-2 victory at Toronto FC.
Both sides had good chances early, with Jack McInerney touching high on a toe-poke attempt and Faryd Mondragon blocking a near post shot from Andre Akpan.
Colorado broke the deadlock on the 63rd minute, with Conor Casey striking from the penalty spot following a questionable foul call inside the box. Danny Califf looked to get a hand on Pablo Mastroeni's shoulder, and the Rapids captain went down under the slight contact.
But the Union leveled just three minutes later, when Danny Mwanga found space from 25 yards out. Center back Drew Moor failed to close the gap, and the second year striker beat Matt Pickens with a shot that snuck inside the left goalpost.
4. July 29, 2011 Colorado 2, Philadelphia 1 (PPL Park)
Goals: Mastroeni 35', Nyassi 45', Torres 90+'
This was Philadelphia's only regular season home loss in 2011.
The Union controlled the bulk of the game, putting 20 attempts on goal to Colorado's 9. Possession was 60/40 in favor of Philadelphia.
After Keon Daniel's free kick hit the post on the 27th minute, Mastroeni scored a golazo for the Rapids. Latching onto a quick throw-in, the Colorado captain beat Carlos Valdes to the inside and hit a left footed curler beyond Mondragon at the far post.
It was a rare moment of offensive brilliance from the defensive midfielder.
The visitors doubled the lead just 10 minutes later, when Sanna Nyassi was able race by the Union backline, pick up a nice throughball, and slot past Mondragon.
Philadelphia had great chances to score but Michael Farfan blazed over the bar from 10 yards out and Valdes was stoned at point blank range by Pickens.
The game was finally put out of reach when Sheanon Williams earned two consecutive yellow cards for dissent. The fullback, on the receiving end of a hard foul, was sent off by the referee after a prolonged argument over the call.
5. March 18, 2012 Colorado 2, Philadelphia 1 (PPL Park)
Goals: Castrillón 56', Cascio 62', Pajoy 71'
Philadelphia's 2012 home opener was a disappointing affair.
Coming off a 3-1 loss in Portland, the new look Union were seeking a quick turnaround at PPL Park.
Colorado, playing a new 4-3-3 formation under first year head coach Oscar Pareja, took the lead on the 56th minute through Jaime Castrillon. It was a midjudgement by Union goalkeeper Zac MacMath, who couldn't hang on to Omar Cumming's left sided cross. Despite getting two hands on the ball, Castrillon was waiting at the back post to tap home the spill.
Fortunes changed with a Larentowicz red card in the 58th minute, which gave the Union a man advantage and 32 minutes to find an equalizer.
But Colorado scored just 4 minutes later, rookie Tony Cascio doubling the lead on a Rapids counterattack.
Lio Pajoy scored his first Union goal to cut the lead in half on the 67th minute, but 10-man Colorado hung on for a 2-1 road win.
Contact Union writer Kevin Kinkead at email@example.com