Although the Saints beat Gloucester in their first match of the season, the trip to Harlequins a week later ended in a 26-13 defeat.
Mallinder has responded by shuffling his back division, with Jon Clarke moving from centre to full-back to replace Greg Tonks and Paul Diggin returning on the wing.
Tom May moves off the wing to take Clarke's place in the midfield, while Ryan Lamb replaces Stephen Myler at fly-half.
Brett Sharman and Tom Mercey come into the front row for Andy Long and Brian Mujati respectively, while the rest of the pack remains unchanged.
Mallinder says that the Saints need to reduce their error count if they are to bounce back with victory over the Exiles.
"We were not good enough at the Stoop and made far too many mistakes against what is a very good Harlequins outfit," he said.
"We will have to cut those out if we are to get a good result against a tough London Irish team tomorrow."
London Irish coach Toby Booth has made two changes to the starting XV that were edged out 30-29 by Sale last Friday.
Adam Thompstone will start on the wing after coming off the bench against the Sharks, while Ed Siggery is handed a full competitive debut at blindside flanker. Marland Yarde and Kieren Roche drop out.
New signing Bryn Evans has been named as a replacement after arriving from New Zealand and academy prospect Anthony Watson is also included on the bench.
Booth said: "We have been competitive in the opening two games and there have been positives to come out of them; however, we want to be winning close encounters when they are there for the taking."
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