LA scored a 3-1 aggregate win following their 1-0 away win in the first leg but it did not come without its problems as Luke Rodgers scored for the Red Bulls in just the fourth minute at The Home Depot Center after a brilliant through ball from Thierry Henry.
The Galaxy rallied thanks to goals from Mike Magee (from a Beckham corner) and Landon Donvan (penalty which Beckham won) abut it was Beckham's influence which received adulation from the coach.
"He's a player with an unbelievable desire to win and compete," Arena said. "When we got down a goal, David helped pick up the team.
"His energy in the second half and earning the penalty it was all David. David, I think, was an inspiration to our team."