The Bees fall to an opening day defeat.
A dogged Barnet side were undone by two quick-fire Leyton Orient goals at the Matchroom Stadium.
The Bees had the better of an end-to-end first half, but created few clear-cut chances in the second period.
Leyton Orient grew in stature as the game progressed, and broke the deadlock with 16 minutes left to play.
Playmaker Dean Cox whipped in a cross from the right hand side, which Jay Simpson fired past Graham Stack at the near post.
With the Bees still recovering from the goal, Orient struck again just a minute later – Paul McCallum nipping in to double the O’s lead.
McCullum looked dangerous throughout the match and could have put Orient ahead after only seven minutes.
As Stack came out of his goal to close down the striker, the former West Ham man’s chipped shot floated just wide of the left-hand post.
But it was Barnet who had the best chances of the game.
With five minutes gone Andy Yiadom showed quick feet in the penalty area, only to be denied a shot after some last ditch defending by Mathieu Baudry.
John Akinde’s powerful run down the left was then beautifully dummied by Yiadom after 15 minutes – the ball fell to Michael Gash in the box, who placed his shot wide of the left post.
Akinde then found himself one-on-one with O’s keeper Cisak, after a through ball from Mauro Vilhete.
The forward slipped the ball across to Curtis Weston from a narrow angle, who fired a shot over on 23 minutes.
Barnet will have been disappointed not to take advantage of their superior first half showing, but will be buoyed by a strong performance against a side relegated from the third tier last season.
The Bees travel to League One Millwall in the Capital One Cup on Tuesday.
BARNET: Stack, Hoyte (Gambin 80'), Johnson, Dembele, N'Gala, Yiadom, Vilhete (Muggleton 66'), Weston, Togwell, Akinde, Gash (Stevens 86').