The Tangerines are riding high in the Scottish Premiership as they sit second following last weekend's narrow 1-0 victory over Ross County at Tannadice.
Danny Lennon's eighth-placed Buddies are their opponents on Thursday but while United are in a rich vein of form with six straight wins to their credit, McNamara is convinced their trip to Paisley promises to be a demanding 90 minutes.
McNamara said: "We will have every respect for St Mirren. They like to get the ball down and play like ourselves so it should be open in that respect.
"We're on a good run of form right now but we know what St Mirren are capable of on their day.
"We'll need to be wary of them and we will be because our aim is to keep this run going.
"There are no easy games in this division and that will definitely be the case when we go through there on Wednesday."
United have been attracting big crowds of late, with over 8,000 witnessing their win against County, so McNamara hopes they travel to Paisley in numbers to roar their side on to another victory.
He said: "We had a great attendance for the County game.
"They can be like an extra man by creating the sort of atmosphere the players respond to on the pitch.
"We're hoping to have a decent-size following through for the St Mirren game because it can make all the difference.
"They're liking what they're seeing from the lads so long may that continue."
United face a hectic festive period with games against St Johnstone and Aberdeen coming hard on the heels of Thursday's clash.
And McNamara said: "The players are relishing it.
"The games are coming thick and fast but we'll just focus on one at a time and see where that takes us.
"St Mirren will be tough to start with but we should be confident going into it given our recent results."
Winger Gary Mackay-Steven has a knock which forced him to miss training on Tuesday but United hope both he and full-back Keith Watson will be fit in time to face the Buddies.