CARSON, Calif. -- Robbie Keane couldn't help himself.

Christian Wilhelmsson's 67th-minute rebound touch off a Landon Donovan shot appeared to be headed -- a bit slowly, albeit -- for the back of the net in Sunday's Western Conference Finals leadoff leg between the Los Angeles Galaxy and Seattle Sounders.

But Keane, the productive Irish striker, just had to jump in and slam the ball behind Seattle keeper Michael Gspurning for the Galaxy's third and final goal in their 3-0 win.

"He was too slow, eh?" Keane joked afterward of Wilhelmsson.

The teams will play again next Sunday in the return leg in Seattle, with the Sounders now needing to outscore the Galaxy by four goals to advance to the MLS Cup in the aggregate-goal playoff system.

Keane has played inspired soccer in this 2012 postseason, with four goals in four matches thus far. The final one Sunday was a bit of a steal from a teammate, but Keane didn't mind. He was just following the words of his youth coaches, he said, and making sure the ball hit the back of the net as quickly as possible.

"This was on its way in, but it's OK," laughed Wilhelmsson, a Swedish international. "He's a striker. That's how they should think. It's better to be there one time too much than one time too little."

The Galaxy's first goal on Sunday, which coach Bruce Arena called "probably the difference in the game," came in the lone minute of extra time of a tightly played first half.

Wilhelmsson deftly pretended to touch Sean Franklin's pass from the right side, letting Donovan get it freely in the box. Donovan tried to create room for a shot, then delivered a short cross directly to Keane's head for his third postseason goal.

After Donovan nearly found Keane again on a sharp sequence in the 57th minute, the Galaxy added a second goal in the 64th. Keane, coming off a long run through the midfield, passed smartly to Franklin to the right and Franklin one-timed a perfect ball to Mike Magee.

Playing to his “Mr. November” nickname, Magee proceeded to calmly knock it past Gspurning's outstretched hands.

"He gave me a layup," Magee said of Franklin.

The Galaxy had three more serious chances for goals, including in the 76th minute, when Donovan's tap-in was kicked out a foot away from the goal line by Seattle center back Jeff Parke.

"You can't have everything in life," Arena said, smirking, in his postgame news conference.

L.A. goalkeeper Josh Saunders was solid, but he was barely challenged. Seattle's two best chances to score came on a strongly hit deep ball from Osvaldo Alonso in the 31st minute and a poor touch from Galaxy center back Omar Gonzalez in the 50th that almost went in for an own goal.

The Sounders, who beat Real Salt Lake on Thursday to qualify for the semis, were without top goal scorer Eddie Johnson until the 64th minute.

Sunday's return leg is scheduled for 6 p.m. PT at CenturyLink Field in Seattle, meaning the Galaxy will get a week’s break, including the next two days off from practices. Having played four games during the past 11 days and five in the past 15, Keane acknowledged Sunday that there were "a lot of tired legs in our camp."

"We've played about 50 games in the last two weeks," midfielder David Beckham said.

In two games in Seattle this season, the Galaxy lost by a combined six goals, 6-0. Seattle coach Sigi Schmid said he and his team "take solace in that fact," recalling their August 4-0 win, started by a sixth-minute strike from Johnson.

"We know we gotta come out with the same sort of effort," Schmid said.

Final notes: Donovan exited Sunday's match in the 84th minute with what he described as a tightening-up of his hamstring. Arena said the team was "hopeful" he'd be fine. … An announced sellout crowd of 27,000 attended Sunday's match, the second straight sellout at the Home Depot Center. Tickets for a potential Dec. 1 MLS Cup final at the stadium against the Houston Dynamo went on sale shortly after the final whistle Sunday. … Galaxy forward Edson Buddle did not suit up Sunday after suffering an unspecified injury during Saturday's training session. His absence in the lineup led to Wilhelmsson's start.