The Saints saw off Sale at Franklin's Gardens last Saturday, relying on seven Stephen Myler penalties and a Ryan Lamb drop-goal to earn the four league points.
But with London Irish only having lost once on home turf in Aviva Premiership this season, Mallinder has said that accuracy and execution will all have to step up several notches if the positive run is to continue.
"Last Saturday was an important win for us," he said.
"As much as you'd like to win with style every week sometimes you have to grind out the result and grabbing your opportunities when you can.
"This is what we did last weekend and although we need the same again in terms of taking our chances we will need to be much better in our all round performance. At times we tried to play too hard last weekend and didn't look after the ball, and we will have to control ourselves more.
"London Irish have a good home record this season, and with some powerful runners out wide like Jonathan Joseph and Sailosi Tagicakibau we will have to be alert defensively.
"They are very organised and as we saw here at Franklin's Gardens in September will play right until the last minute. And in Tom Homer they have one of the best goal kickers in the Aviva Premiership.
"But the spirit in training has been good this week and we are feeling positive ahead of the trip to Reading."
Meanwhile, Declan Danaher returns to the London Irish back-row and Topsy Ojo returns on the wing with Dan Bowden moving to inside centre.
Adrian Jarvis and Ross Samson form the half-back combination.
Matt Garvey moves to the second row with Danaher and Hala'ufia returning to the back-row alongside Richard Thorpe.
"We were bitterly disappointed with our performance last Saturday and this has given us strong focus for training this week," said London Irish head coach Toby Booth.
"The Premiership table is tight with only six points separating fourth and eighth positions. There is still a lot of rugby to be played and there is still everything to play for."
London Irish: 15 Delon Armitage, 14 Topsy Ojo, 13 Jonathan Joseph, 12 Daniel Bowden, 11 Sailosi Tagicakibau, 10 Adrian Jarvis, 9 Ross Samson, 8 Chris Hala'ufia, 7 Richard Thorpe, 6 Declan Danaher; 5 Matt Garvey, 4 Nick Kennedy (c) 3 Faan Rautenbach, 2 David Paice, 1 Max Lahiff.
Replacements: 16 James Buckland, 17 Clarke Dermody, 18 Paulica Ion, 19 Kieran Roche, 20 Jebb Sinclair, 21 Tom Homer, 22 Jonathan Spratt, 23 Darren Allinson.
Northampton: 15 Paul Diggin, 14 Vasily Artemyev, 13 George Pisi, 12 James Downey, 11 Noah Cato, 10 Stephen Myler, 9 Martin Roberts, 8 Roger Wilson, 7 Calum Clark, 6 Samu Manoa, 5 Christian Day, 4 Mark Sorenson, 3 Paul Doran-Jones, 2 Andy Long, 1 Soane Tonga'uiha.
Replacements: 16 Ross McMillan, 17 Alex Waller, 18 Brian Mujati, 19 James Craig, 20 Ben Nutley, 21 Ryan Glynn, 22 Ryan Lamb, 23 Tom May.
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