Neagle's goal was his fifth of the season.
The Sounders (6-4-3, 21 points) took a 1-0 lead in the ninth minute on a goal by Andy Rose before Camilo Sanvezzo scored a pair of first-half goals for the Whitecaps (4-5-4, 16 points).
Servando Carrasco converted a penalty kick in the 70th minute, lifting the Sounders into a 2-2 tie. Neagle factored into that one, as well, when he was taken down in the right side of the penalty area by Vancouver's Greg Klazura. Referee Hilario Grajeda immediately pointed to the spot, and Carrasco launched the kick into the upper left corner over the outstretched hands of goalkeeper Brad Knighton.
Carrasco's PK, in front of 53,679 fans at CenturyLink Field, was his first MLS goal.
Midfielder Rose put the Sounders on the board at the outset of the ninth minute. Neagle, playing just on Vancouver's side of the midfield circle started the play, sending a through ball toward the right side. Rose broke behind the Whitecaps defence, took it alone into the penalty area, and sent a 15-yard shot into the back left corner for his first of the season.
Sanvezzo's goals in the 10th minute and the 26th were both assisted by Russell Teibert. Sanvezzo has five goals on the year.