Ms Collins resigned three weeks before the election after an email emerged that suggested she was involved in a plot to undermine former Serious Fraud Office boss Adam Feeley when she was Police Minister.
A high-level government inquiry is investigating the email and her relationship with Mr Feeley.
An apparent backlash in Papakura saw Ms Collins' 2011 majority dive from 9890 to 4851 -- still a convincing victory, but a sizeable dent.
The party vote held firm, falling slightly from 52.6 per cent of the total vote in 2011 to 52.2 per cent. More people gave their party vote to National than gave their electorate vote to Ms Collins (15,705 v 14,001).
Her electorate had minor tweaks after last year's boundary changes, but the result will be seen as significant voter blowback.
Many questions have swirled around Ms Collins this year, including the Oravida affair, her attack on and subsequent apology to journalist Katie Bradford, and the passing of a public servant's details to Whale Oil blogger Cameron Slater, whose attack blogs subjected the official to death threats.
Prime Minister John Key has not ruled out a possible return to the Cabinet table for Ms Collins, but it would not be considered until well after the inquiry has reported its findings to Mr Key on November 28.
Saturday's result delivered a resounding victory for Maurice Williamson in Pakuranga, a seat he has held since 1987. His majority of 13,846 in 2011 was shaved to 11,905.
Mr Williamson fell on his ministerial sword in May after the Herald revealed his intervention in a police inquiry into businessman Donghua Liu, who has donated tens of thousands to National and Labour.
By Derek Cheng of the New Zealand Herald
