SEATTLE — If the clock was still running, the Seattle Sounders and Los Angeles Galaxy would surely still be trading goals. But the whistle did blow, and on Sunday afternoon it did so with the Sounders defeating the Galaxy, 4-3, in front of 46,673 at a raucous CenturyLink Field.

Cristian Roldan scored the game-winner at the back post in the 89th minute, tracking down a cross from late substitute Brad Smith to put the Sounders on top for a third and final time on the afternoon. It was Roldan’s second goal of the match and his sixth of the season.

The victory catapults the Sounders (13-8-7, 46 points) from fifth place to second place in the Western Conference playoff race. They have now won back-to-back matches against two of their biggest rivals after struggling through a four-game winless streak.

For their part, the Galaxy (13-12-3, 42 points) have now posted just one win in their last seven matches and sit in sixth place in the West.

Roldan’s dramatic game-winner capped a wild stretch of soccer that saw the teams combine to score five goals in 23 minutes.

Raul Ruidiaz opened the scoring in first-half stoppage time. The Peruvian striker found himself unmarked at the back post to knock in a cross from Nicolas Lodeiro, who had initially gathered a weak clearance at the edge of the penalty area. It was the 12th assist of the season for Lodeiro. It was also the 11th goal of the year for Ruidiaz, who has posted three goals and two assists in the Sounders’ last three matches.

The Sounders flew out of the gate to start the second half, and Roldan doubled the lead in the 55th minute, collecting a deflected corner kick at the edge of the penalty area, deftly sidestepping defender Giancarlo Gonzalez, and burying a left-footed shot past goalkeeper David Bingham.

With less than 30 minutes to play and the Galaxy looking fairly flat, it seemed the Sounders were on their way to a relatively routine victory.

But then the visitors earned a corner kick, and Zlatan Ibrahimovic scored his 23rd goal of the season, outmuscling Gustav Svensson to send a 66th-minute header past goalkeeper Stefan Frei.

Uriel Antuna scored a bit of a fluky equalizer in the 75th minute, gathering a deflected cross at the edge of the 6-yard box and easily besting a flat-footed Frei.

Jordan Morris responded for the Sounders just two minutes later after a quick give-and-go with Ruidiaz left Morris one-on-one against Bingham for a simple finish and the 3-2 lead.

The Galaxy equalized for a second time in the 81st minute when Diego Polenta found Jorgen Skjelvik with a ball over the top. Skjelvik tracked down the lob to the left of the penalty spot and tied the match at 3-3 with a first-touch shot.

It seemed the Galaxy might escape with a critical point, but Roldan and the Sounders had other ideas.

Looking forward, the Sounders visit the Colorado Rapids on Saturday, while the Galaxy visit the Rapids the following Wednesday.

Man of the Match

Cristian Roldan. A brace and a game-winner.

Moment of the Match

The Ibrahimovic header. It was Zlatan’s seventh goal in the Galaxy’s last four matches, and it ignited a 23-minute fireworks show.

Match to Forget

Giancarlo Gonzalez committed two errors that led to Sounders goals on a night when the Galaxy defense was poor once again.