The victory puts Washington (13-0-1) in the District 12 AAA title game Thursday against the winner of Wednesday's Catholic League final between La Salle and Father Judge.
If the Eagles' near-perfect record suggests they waltzed to the league title, their first since 2009, think again.
The team lost five players - three starters and two top reserves - during this season, including its starting goalkeeper and two others who were expelled from the school, because of an altercation, with one game remaining in the regular season.
Coach Chris Reid was forced to call up several junior-varsity players and plug in a new goalie, 6-foot-5 sophomore Danniil Paraskevov.
In four games in net, Paraskevov, who made seven saves Tuesday, kept the offensively potent Eagles, who outscored opponents by 58-17 this year, in contention.
"We gutted it out," Reid said. "We went through a lot of adversity this year."
Mimbar put the Eagles up in the 24th minute, sliding the ball past Vikings keeper Howard Lynn with an assist from forward Seriah Wogbeh.
Washington took that 1-0 lead into halftime, but Northeast (11-2-1) found the equalizer on a goal by Kevin Kureta in the opening minute of the second half.
Mimbar's winner was his 27th goal of the year, one shy of the school record of 28 held by current Father Judge coach John Dunlop.
"Really the credit goes to Mohamed [Conde] to make that pass," Reid said.
Credit the coach for a brilliant personnel adjustment that moved Conde to midfield and senior Duke Gbolue to forward. That switch drew Northeast's most dynamic player, Chris Black - who had marked Conde throughout the team's regular-season encounter, a 1-1 draw - away from his front line to open space for Mimbar.
The Vikings lost their second straight title game. Washington had last gone undefeated en route to a league title in 1984.
"Some boys were slacking on the team," Mimbar said, "but me as a captain got in their face and told them the deal. We've got to win this."
Northeast 0 1 – 1
Washington 1 1 – 2
Goals: W-Wilo Mimbar 2; N-Kevin Kureta.
Saves: W-Danniil Paraskevov 7; N-Howard Lynn 5.
Contact Evan Burgos at firstname.lastname@example.org.