KARL Robinson was left fuming over the opening goal Oxford United conceded in their Emirates FA Cup defeat to Peterborough United.

The U's lost 2-1 in the first-round tie at the Kassam Stadium, where the big talking point was when Siriki Dembele put the visitors in front midway through the half.

Both managers agreed the offside flag should have gone up, but after Josh Ruffels - who went on to score the equaliser - took a loose touch, the Posh front man raced away to score.

"The assistant referee said he wasn't interfering," Robinson said.

"He doesn't have to make contact with Ruffs to be in play.

"He's clearly close enough to be active. 

"He made a run off Ruffs' shoulder. The ball's meant for him, which meant Ruffs has had to defend the ball."

Posh boss Darren Ferguson agreed.

He said: "I haven't seen it back, but I was told it was offside and the linesman's got it wrong.

"I thought the officials had a poor day and we have got fortunate."

After getting back on level terms before the break, Peterborough went on to win the game when Jack Taylor's 62nd-minute shot deflected in.

Robinson was encouraged generally with the display and felt his players deserved better.

He said: "I thought we were sloppy in the final third.

"We got into some areas and wasted opportunities when we could have done better.

"But we've been done by an offside goal and a deflection. You're left with a bitter taste in your mouth.

"It's infuriating, because it seems every time we go in the opposition's box every bounce is going the wrong side of us.

"We played well, we gave a good account of ourselves.

"That's that competition put to bed for another year and now it's on to the league."