There were seven tries in a thrilling match which Northampton won 30-23 thanks to a last-gasp try which originated from a charge down.
Northampton went ahead first through wing Noah Cato but found themselves 18-11 down at half-time as home wing Sailosi Tagicakibau and full-back Delon Armitage contributed tries.
But the Saints were on the march after the break and went 23-18 up at one stage as number eight Roger Wilson and full-back Paul Diggin added touchdowns, all three of Northampton's tries coming via outstanding work from goal-kicker and fly-half Stephen Myler.
Exiles favourite Declan Danahar levelled the match at 23-23 with a corner try before Armitage was charged down by centre George Pisi and replacement Ben Nutley took a pass from 'no-miss' territory to score under the posts and win the game with a try bonus point.
West said: "We were totally focused on London Irish today. We thought that if we turned up here and were physical that we could do a job on them and that is how it proved.
"We made a few mistakes in the first half and, with a team with so much threat out wide as London Irish, if you give them any loose ball or concede some momentum, they are going to hurt you - and that is how it proved in the first half.
"If we tightened up a bit, it would come our way. Myler controlled the game well. He missed a few kicks at goal that would have made us comfortable but, on the whole, he is the same as everybody who all played well today.
"He has played consistently well for us recently and has been worth his place in the team.
"Of course, we are disappointed with certain aspects of our game where we gave them easy points to get into it but we dug in and did what we had to do to win."
London Irish head coach Toby Booth had apologised to the fans who made the long trip to Newcastle last week only to see them lose to the Premiership's basement club.
But there was far more endeavour and fight in them this week, and he is not giving up on a Premiership play-off place yet.
Booth said: "While it's mathematically possible, we are never going to stop fighting for it and that's ultimately what we are here to do.
"The performance today needed to be better, given what went on before. There was a lot of remorse shown by players for the performance in Newcastle despite very difficult conditions.
"Today, our physicality was outstanding, which it had to be against Northampton. Everyone will agree that it was a fantastic contest. It was everything that was good about the Premiership but we are bitterly disappointed with the outcome.
"We search every week for the one per cent that is going to make a difference and how we start the game is important which is what happened today."
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