Josh Saunders made five saves to earn his ninth shutout in 19 matches this season for the Galaxy, who beat the Red Bulls for the first time in 2011, after a 1-1 tie in May and a 2-1 loss earlier this month in New Jersey.
"We seemed very comfortable playing here," Saunders said. "It's great to get a win right off the bat. We now just have to go out and try to win again."
Magee, who began his career with the Red Bulls franchise, played six seasons with the team as both the MetroStars and Red Bulls and then was traded to the Galaxy in 2009. He got past the defense on a 45-yard pass from Beckham. While most of New York's players stood and watched, thinking the play was offside, Magee pushed it past Red Bulls keeper Frank Rost.
"The ball was a perfect pass," Magee said. "I was 100 percent not offside. Besides, it wasn't called, so then it wasn't. I was just glad to get it."
"Mike is a good player who for the majority of his career has always been good around the penalty area," said Galaxy head coach Bruce Arena, who also coached Magee with the MetroStars and engineered the trade that brought Magee to Los Angeles. "As he's matured as a player, he's been able to handle a variety of roles and did it all for us this year. He's a very diverse player."
Magee came in and played goalkeeper June 25 in a win over San Jose, making six saves in net after the Galaxy's top two netminders went down with injuries. He did not allow a goal in his brief stint.
Red Bulls head coach Hans Backe, pleased for the most part by the way his team performed, was disappointed that the Red Bulls didn't complete the play on Magee's goal.
"We had about seven guys call for the offside and I believe Keane was offside," Backe said. "Magee came in as a late runner and he made the play. You can't give away a goal like that. You have to keep playing and be more confident. It's a tough goal to give away."
The Galaxy almost scored in the 12th minute when Keane fired a shot that clanked off the right post. Magee was in front to head home a rebound, but his attempt sailed over the crossbar. Red Bulls forward Thierry Henry had a chance in the 22nd minute, when his scissors attempt sailed high toward the goal, but Saunders punched it away at the last second.
New York's best chance to score came in the 49th minute, when Dane Richards swerved through two defenders to put a pass across to Luke Rodgers. But Rodgers' shot was deflected by Saunders' right hand and the ball sailed over the crossbar before Rodgers could get to it.
"I was just trying to see the play," Saunders said. "It was a quick reaction more than anything, ball to hand. I was lucky to get a hand on it. It came off very quick."
Rost made a brilliant save in the 55th minute, keeping the lead at one goal, when he stopped Landon Donovan on breakaway attempt. Donovan was in alone, but Rost made a fine right-handed save on Donovan's shot.
The Red Bulls had an opportunity to tie the match with under 2 minutes remaining in regulation, but Mendes' header off a corner kick from Rodgers went over the crossbar. In stoppage time, the Red Bulls came close again, when Rafa Marquez sent a shot from 25 yards out that Saunders made a diving stop on, with the rebound attempt sailing wide right. It marked the first time the two teams met in the MLS Cup playoffs since the 2001 quarterfinals, a series won by the Galaxy in three games.
The game was marred by a postgame incident involving four players, two from each team. Donovan apparently said something to Marquez, who then took the ball and fired it at Donovan. In the scrum that ensued, Galaxy midfielder Juninho threw a punch at Red Bulls defender Stephen Keel. Referee Alex Prus issued postgame red cards to both Marquez and Juninho, suspending both for the next game on Thursday.