If proof were needed that League One will provide Pompey with a stern test, it was provided at Oxford.
The Blues were holding their own in the first half and were unlucky not to be ahead at the break, with Brett Pitman’s header controversially ruled out.
But Wes Thomas, Gino van Kessel and Josh Ruffels all struck in the second half to leave them with nothing.
And Danny Rose knows that sides are more likely to capitalise on sloppy play now that Pompey are playing at a higher level.
The midfielder said: “It was a frustrating day. It was pretty even at half-time and they hadn’t caused us many problems.
“We had a few opportunities ourselves and we knew that being goalless at the break wouldn’t be the worst position to be in.
"We saw the quality of the opposition we’ll come up against in League One and if you make mistakes you’ll be punished more often."
“At that point we felt we could go on and get a positive result, but it wasn’t to be and we ended up conceding an early goal.
“It’s disappointing because the same thing had happened at Cardiff in the cup earlier in the week. It gives you a mountain to climb.
“We saw the quality of the opposition we’ll come up against in League One and if you make mistakes you’ll be punished more often.
“Hopefully we can get back to winning ways against Fulham on Wednesday, so we can go into the next league game full of confidence.”
Rose was joined in the centre of midfield by Adam May and believes the teenager has a bright future.
He said: “He’s shown that he can hold his own in the team at that level. Playing in these games can only aid his development.”