Saints needed a late Ryan Lamb penalty to edge Gloucester 26-24 at Franklin's Gardens last Sunday, after they had squandered a 23-13 advantage.
Their next test comes against a Quins side who also tasted victory in their opening Aviva Premiership fixture, fly-half Nick Evans kicking seven from seven in a 29-24 success over London Irish at Twickenham.
Director of rugby Mallinder has moved Tom May on to the wing as Jon Clarke comes into the midfield for the journey south, while prop Alex Waller and lock Christian Day replace Paul Doran-Jones and Mark Sorenson up front.
And while Mallinder was delighted with the way his players dealt with falling behind late in the game against the Cherry and Whites, he acknowledges they have faced a tough week with the short turnaround between fixtures and knows Amlin Challenge Cup holders Quins pose a real threat.
"It was good that the players kept their composure," he said. "(Captain) Phil Dowson and the rest of the team had a chat under the posts after we went behind. Four minutes is a long time and they concentrated on getting hold of the restart and taking the opportunity when it came.
"It's been a tough week this week, a short week, but sometimes that's not a bad thing and the important thing is that by Friday night we're fully motivated, prepared and feeling fresh.
"It's going to be a tough challenge. Harlequins played well last week against London Irish. They're a good side who have been together all summer with few disruptions from the World Cup.
"They have also put us under pressure over the past couple of years and of course came to Franklin's Gardens and won in a tight game last season. So we know what they can offer, and they have some key players who can win the game for them."
Harlequins director of rugby Conor O'Shea, meanwhile, has made just two changes to his line-up, with Tim Fairbrother coming into the front row and Chris York replacing the injured Tom Guest at number eight.
Saints triumphed at The Stoop at this exact stage last term, and former Ireland international O'Shea wants the club's vociferous support to help his side avoid a repeat in their first home outing of the campaign.
He said: "One of the many positive aspects from last season was just how vociferous our support was at The Stoop, and there is no doubt, as we look to challenge at the top end of the table in all competitions, that support will become an integral part of our success.
"The more difficult The Stoop becomes to visit for opposing teams the better, but we know as a group it is up to us to play the type of rugby with and without the ball that makes people really get behind us."
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