A first minute penalty from Bobby Zamora and a stunning strike from Mark Yeates on 17 minutes completed the scoring on the night as the second string turned on the style in the first half at Stevenage.
However, a young Pompey side did not cave in and the second half became a rather scrappy affair that never looked like reaching the heights of the first.
"They started the game exceptionally well and got themselves into a good position but, I feel as the game wore on, we went away from what we are really about in terms of the way we passed the ball and moved," commented Clive afterwards.
"It got frustrating and at times we forced the issue rather than play with the ability we have. Portsmouth kept going, they were game and a young side.
"In reserve football you have these encounters where, unless you do it very well, you pay the price for that. Our second half performance was very disappointing."
Asked whether he took considerable heart from the manner of the opening spell, Clive explained that the standard is the expectation level that he knows the team are capable of.
"I'll be honest, I try to set those standards every day in training and you can see day to day exactly what they are capable of. That is what we are looking for them to produce on a regular basis in the games.
"They are trying to do that and certainly did from the start of the game but, as I say, it fell away in the second half and that was the disappointing aspect of the evening."
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Reserve coach Clive Allen was disappointed with the second half performance of his side against Portsmouth on Monday following a start to the game that he described as exceptional.