The Tannadice club savoured their first win of the new Scottish Premiership campaign by beating Saints 4-0 and now turn their attention to their tricky second-round tie away to the Scottish Championship side this evening.
And McNamara, in his first full season at the helm, believes his players have given themselves the ideal platform going into the clash with Dumbarton.
He said: “There were so many positives to take from Saturday’s result against St Johnstone. Both the result and the performance was what we were looking for.
“Now we have to try and move on from there when we go to Dumbarton in the cup.
“The lads are feeling good after that. They’re looking forward to the next game and it’s one where we want to see a good performance and a positive result.”
McNamara is taking every precaution to ensure there is no upset. Ian Murray’s side beat Morton 3-1 on Saturday.
He said: “We’ve watched them so know they’re a decent side. They had a very good result against Morton last weekend. We will be in for a typical cup tie. It won’t be easy, so it’s up to us to go about our business well.”
United hope winger Ryan Dow shakes off a leg strain in time to play but they have no other injury worries and Turkish winger Nadir Ciftci could come into contention for a start. Defender Gavin Gunning completes his two-match ban.
Dumbarton manager Ian Murray believes he has the attacking menace in his side to trouble United at the Bet Butler Stadium if he can get them fit enough to take the field.
The Sons’ new recruit, former Dunfermline, Kilmarnock, Hibs, Hartlepool and Dundee striker Colin Nish will lead the attack but Murray is not sure who will be supporting him. Chris Turner is a doubt, as is the creative Scott Agnew, winger Mark Gilhaney and former Aberdeen striker Mitchel Megginson.
Murray said: “With the addition of Colin last week, I believe we have a midfield and front line that when we go forward are as strong as any in this Division.
“It would be great to have them tested against a Premiership side. However, it will be close to kick off before I know what my line up will be.”