We just didn't perform today. Our wide players couldn't get past their full-backs, ad we didn't create chances," Robson said after the 1-0 defeat at Fratton Park.
"Their pitch didn't help the game, it was scrappy and I think a draw would have been a fair result.
"Our away form is a worry, we just don't create enough chances.
"We need to start playing away like we do at home."