The Jags will face a resurgent Sons side who have started to claw themselves back into survival contention under new manager Ian Murray thanks to recent wins over Falkirk and Morton.
In contrast, Thistle's surge to the top of the Scottish game's second tier has suffered a mid-season stutter as the Maryhill men have won just twice in their last six league outings.
And McNamara was in no mood to underestimate the size of the challenge that awaits his side at the Bet Butler Stadium.
He said: "I think the game is a sell-out and that will probably build a cup-tie atmosphere that will no doubt give Dumbarton a lift.
"By all accounts they were very unfortunate not to take something from their last game against Dunfermline and before that they beat Falkirk and Morton so they are very much on an upward curve.
"But we will go to Dumbarton looking for all three points and trying to win them in the correct manner. The last two games have been a bit frustrating.
"Against Airdrie in the first-half we did not pass the ball that well but came onto a much better game after the break.
"At Livingston, it was the other way around and to be fair to Livi they finished stronger than us.
"Although to lose the goal at the death after Sean Welsh was sent off was very frustrating.
"So this is very much about putting together a complete performance and doing everything we can to get back to winning ways after these two draws."
As a result of that red card, Welsh is suspended for the trip to the Rock, but Thistle are otherwise at full strength.
Returning his attention to tomorrow's tussle, McNamara – boosted by the signing of goal machine Steven Craig – seemed to hint that width will be a weapon in his game plan for the Sons test.
The Jags boss said: "The pitch at Dumbarton is a good surface with plenty of width and that is something we have to make the most of.
"So we will be looking to move the ball at a good tempo and really try and impose our game on Dumbarton.
"But it is a game we are all looking forward to and with the element of a local derby about it there should be a really passionate atmosphere."
