Skipper Lee Frecklington was shown a straight red card as Lincoln slipped to their first defeat of the season at the hands of Crawley.
Frecklington was dismissed nine minutes into the second half for a late and rash challenge on Mark Connolly.
By then, the Imps were one goal down after Michael Bostwick's own goal in first-half added time.
That proved to be the only goal as Crawley recorded a surprise win in front of new manager Gabriele Cioffi, who was watching from the stands.
Town controlled the first half with Panutche Camara forcing Grant Smith into the good save, and the Imps should have taken the lead a minute before the break when John Akinde poked wide from close range.
It proved to be a costly miss as Felipe Morais's deflected cross was inadvertently turned into his own net by Bostwick.
Despite Frecklington's red card, Lincoln dominated the remainder of the match, but couldn't force an equaliser.
Match report supplied by the Press Association.
