Jakob Glesnes unleashed a stunning winner from 25 yards out in the third minute of extra-time stoppage time on Saturday as the Philadelphia Union downed New York Red Bulls 1-0 in the first round of the MLS Cup playoffs.

Norway's Glesnes came to the rescue of the second-seeded Union, who were unable to capitalize on their sharper play over 90 minutes and had plenty of worrying moments in extra time.

New York struggled to create chances throughout, failing to register a shot on goal until Patryk Klimala made his way behind the Union backline to force Andre Blake into a save in the 95th minute.

Kyle Duncan also had a near-miss in the second half of extra time, his effort from inside the area glancing off the left post.

The match looked to be heading for a penalty shootout after Red Bulls keeper Carlos Coronel saved a shot from Sergio Santos and New York's Andrew Gutman's tackle denied Cory Burke directly in front of Coronel's goal.

From a free kick on the left the ball finally fell to Glesnes. He chested the ball down and, with his second touch, belted his long-range arcing shot out of reach of Coronel and into the net.

According to MLS, it was the latest goal scored in any game in the league's 26-year history.

It sparked massive celebrations at Subaru Park, where an hour before the game the Union announced that Jamiro Monteiro and Olivier Mbaizo were sidelined because of MLS's Covid health.

The team detailed the variety of reasons players could be ruled out under the protocols apart from a positive test, but didn't say which applied to Monteiro and Mbaizo, who were recently playing for their national teams, Cape Verde and Cameroon, in African World Cup qualifying. Both arrived back in Philadelphia this week.

It is the second time in three years that the Union have beaten the Red Bulls in the opening round of the playoffs, which continued Saturday with Sporting Kansas City's 3-1 victory over the Vancouver Whitecaps in a Western Conference clash.

Khiry Shelton and Nicolas Isimat-Mirin scored first half goals and Graham Zusi added a third in the 58th minute for hosts Kansas City.

Cristian Dajome converted a penalty for Vancouver that briefly knotted the score at 1-1, but the visitors couldn't come up with another goal.

The New England Revolution in the Eastern Conference and Colorado Rapids in the West are the top seeds in the playoffs and enjoy first-round byes.

The Revolution -- who won their first Supporters' Shield as the team with most regular-season points -- will face the winner of Sunday's match between New York City FC and Atlanta, while Philadelphia will face either Nashville or Orlando in the second round.

The Rapids await the winner of Sunday's match between Portland and Minnesota.

The league will see a new MLS Cup champion crowned this season after 2020 champions Columbus failed to make the playoffs.