Wayne Rooney scored the winning goal on a penalty kick in extra time against Philadelphia. (Jonathan Newton/The Washington Post)

With Audi Field drenched by rain, D.C. United and the Philadelphia Union clashed last week for almost two hours without producing a goal. Then, in the final minutes of extra time, the U.S. Open Cup game swung through every possible outcome with an eruption of scoring.

After the Union scored in the 113th minute, a win for the visitors seemed likely. But then D.C. United’s Chris McCann headed in the tying goal in the 118th, which seemed to suggested the game would be decided by penalty kicks. And in fact, it sort of was: Wayne Rooney produced the winner on a penalty kick in the 120th minute after Luciano Acosta drew a foul in the penalty area.

The win sent United to Wednesday’s round-of-16 match against New York City FC at Audi Field in a theatrical fashion surprising only to those unfamiliar with the team’s U.S. Open Cup history.

Since 2012, when the tournament changed its rules to grant MLS teams automatic qualification, United has played 16 Open Cup matches with just eight decided in regulation. Four needed extra time, and another four went to penalty kicks. No other club that has been part of MLS during this span has had a higher percentage of Open Cup games extend beyond 90 minutes.

“Now I'm going to have to think about that all night,” United Coach Ben Olsen said when told of his team’s outlier status. “I don't know. I don't know why. We do tend to make these Open Cups very eventful.”

In this tournament, which includes amateur and professional teams, MLS clubs enter in the fourth round, when 32 squads remain. For the games played after that point — from 2012 until now, including this year’s fourth-round matchups — about 15 percent require extra time, and another 12 percent go to penalty kicks. D.C. United far exceeds both those marks.

The Union ranks second on this Open Cup drama metric, with 41 percent of its games extending to extra time or penalty kicks. So when those two clubs met in this tournament last week, more than 90 minutes of soccer at Audi Field seemed fitting.

Steve Birnbaum, a D.C. United defender since 2014, associates Open Cup games with a long grind and said he wasn’t surprised to play an extra 30 minutes against Philadelphia.

“They’re always weird, especially the first rounds,” Birnbaum said of games in this tournament. “One of those things where calls could go either way.”

Last year, United won its first game on penalty kicks before Orlando City eliminated D.C. in the next round’s lightning-delayed match, which also required penalty kicks.

Physically, the difference between a 90-minute game and one that goes to extra time can be jarring. Players wear tracking devices, and Birnbaum said what’s usually 10,000 meters (6.2 miles) run during a 90-minute game turns into something closer to 12,000 (7.5 miles).

“It doesn't seem like a big difference, but your body is used to going 90 minutes game in and game out,” Birnbaum said. “Then when you go 120, it takes a toll.”

The Colorado Rapids sit at the other end of the spectrum. Eleven of their 13 matches since 2012 have taken just the usual 90 minutes to determine a winner. The Los Angeles Galaxy and the Portland Timbers have each played 17 Open Cup games during this stretch but never one that required penalty kicks.

Frequently in this tournament, teams might choose to hold out usual starters, with their focus on upcoming MLS games. But with MLS in a dark period of its schedule, United played many regular starters against Philadelphia and plans to do so again this week, Olsen said.

Thanks to international duties, the team is missing American winger Paul Arriola (Concacaf Gold Cup) and Venezuelan midfielder Junior Moreno (Copa America). But midfielder Chris Durkin should play after returning from the under-20 World Cup in Poland and then missing last week’s game because of a suspension from his red card in this tournament last year.

The Open Cup limits game-day rosters to five international players, and Olsen will be mindful when it comes to players who have recently dealt with injuries. Starting goalkeeper Bill Hamid, who has a minor knee injury, didn’t train with the team Monday; midfielder Russell Canouse and defender Donovan Pines practiced fully and could be available.

“As much as we certainly want to advance and put the best team forward, we also have to be smart about how we push certain guys that aren’t 100 percent,” Olsen said Monday. “That’s a delicate balance that we’ll figure out over the next day or two.”

Part of the value of Wednesday’s game against New York City arises simply from how it fills a void in the schedule. United’s MLS slate won’t resume until June 26, so another round in the Open Cup helps keep players sharp — maybe for an extra 30 minutes of play and some penalty kicks, too.