The inconsistent display, however, left him with plenty to think about.
McRoberts is clear in his targets for Portsmouth this season and they include promotion.
He knows they will have to play a lot better if they are to achieve their aims, though, and will hope he sees progress.
The coach said: '˜It is good to start with a win but there were aspects of the game I wasn't happy with. WeÂ didn't quite execute our game plan as well as can.
'˜In the end we left three or four tries out on the pitch. There is a need for greater patience at times.
'˜We created good try scoring opportunities but let them slip from our grasp.
'˜Petersfield are a young well-organised team and were always going to be difficult opponents.'
Winger Tom Hopkins was the first to get over the line for the hosts and Lee Chandler converted.
Petersfield hit back with an unconverted try midway through the half.
The home side showed an improvement at the start of the second period.
But it was a penalty that gifted Petersfield an 8-7 lead after 55 minutes.
Two good scoring chances were wasted by Portsmouth until finally they managed to get their noses back in front to lead 14-8 with eight minutes left to play.
They set up a good driving maul and the referee awarded a penalty try when Petersfield stopped it illegally.
'˜The most positive aspect for me was our defence,' added McRoberts.
'˜Petersfield had a lot of possession but we looked solid.
'˜I was hugely disappointed though with the number of penalties we gave away.
'˜We must have been penalised at least 20 times.Â That is a minimum of 200 metres conceded in a game.
'˜It is something we need to focus on. The game only re-affirmed what we already knew about how difficult this league is.
'˜To get out out of it you need to be on your game every week.
'˜Winning after not playing very well has to be encouraging.
'˜We now have to make sure we improve things against Trojans in our next game.'