Strikes from Robbie Keane and Michael Stephens weren't enough to keep the Galaxy from settling for a draw against the league's worst side.
With the tie, the Galaxy are now five points behind Seattle for the Western Conference's top seed, and just four points up on sixth-place Dallas — the first team on the outside looking in at the playoffs.
Keane's lethal chemistry of late with strike partner Landon Donovan created the opener just seven minutes in. Donovan attacked open space in the box before leaving a back heel for Keane, who evaded Dejan Jakovic's challenge before putting home his 13th goal of the season.
United equalized in the 39th minute. Collecting a long D.C. clearance, Galaxy center back Omar Gonzalez casually settled the ball before having his pocket picked by Pontius, who rounded goalkeeper Jaime Penedo and converted. It was the first goal from the run of play for the injury-plagued Pontius since Sept. 15, 2012.
After losing right back A.J. DeLaGarza to a first-half elbow injury, the Galaxy removed Donovan at halftime with an ankle ailment.
The Galaxy appeared to grab the winner in the 81st minute when Stephens collected a pass from Keane and placed a 20-yard shot into the bottom corner.
But United drew level three minutes later, with Porter slipping behind the Galaxy defense and nodding in a Perry Kitchen chip.