Aaron Mokoena broke Coventry hearts with a last-gasp winner at the end of extra-time to hand cash-strapped Portsmouth and a place in the fourth round of the FA Cup following the 2-1 win.
Stephen Wright's 90th-minute own goal had already handed Pompey a lifeline and sent their third round replay into extra-time after Leon Best's superbly taken half-volley had broken the deadlock midway through the first half.
But the 2008 winners were kept at bay by Sky Blues keeper Keiren Westwood until substitute Mokoena headed home with virtually the last touch of the game.
Midfielder Barry Ferguson's first goal for Birmingham was sufficient to seal a 1-0 victory over Nottingham Forest in their third round replay at St. Andrews and clinch a visit to Everton.
Alex McLeish's £1million summer capture from Rangers broke the deadlock 16 minutes into the second half and earned a fortunate victory for the home side.
Blues fielded a full strength side but were often second best against a Forest team which showed seven changes from the line-up that had overcame West Brom on Friday.
Super-sub Jamie Ward helped fire Sheffield United into the fourth round as QPR made their familiar early exit despite a late rally in the 3-2 clash.
The Blades were clinging onto Lee Williamson's early opener when Ward scored with his first touch and then immediately set up a third for Richard Cresswell. A late Rangers comeback, courtesy of Akos Buzsaky's penalty and Damion Stewart's header, set up a nervy finish but the hosts were unable to arrest their dismal FA Cup record.
Derby scraped into the FA Cup fourth round (5-4) on penalties (following a 1-1 draw) but another poor display would have done little to ease the pressure on manager Nigel Clough.
Substitute Gavin Williams grabbed a 92nd-minute equaliser as Bristol City earned a third round replay following their 1-1 draw against Coca-Cola Championship rivals Cardiff.
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