Winger George Boyd grabbed the winner for Peterborough as Roy Keane's poor start to the season continued with a 2-1 loss for Ipswich at London Road.
Keane's Town side took the lead in the Carling Cup second-round tie through new signing Tamas Priskin but the £1.7million striker then missed a penalty.
Lee Frecklington crashed Darren Ferguson's side level with a fine goal before Boyd ensured that Keane is still looking for his first win of the season.
Port Vale made it a Steel City double in the Carling Cup as they eased into the third round with a comfortable 2-0 win against 10-man Sheffield Wednesday.
Micky Adams' side claimed the scalp of Wednesday's bitter rivals Sheffield United in the first round and were always in command against the Championship outfit.
Their cause was helped by the first-half dismissal of Francis Jeffers for what appeared to be a head-butt on Vale midfielder Tommy Fraser, and two goals in three second-half minutes from Kris Taylor and Robert Taylor earned them victory.
Goals from Hogan Ephraim and Wayne Routledge eased the pressure on QPR manager Jim Magilton as brave Accrington bowed out of the Carling Cup at the second-round stage with a 2-1 defeat.
Ephraim pounced for the winner in the 68th minute and Routledge made sure in the last minute before Michael Symes netted a consolation goal for Stanley in stoppage time.
Chris Brown scored twice after Nicky Adams' opener as Preston came from behind for a hard-fought 2-1 victory over Coca-Cola Championship rivals Leicester.
Daniel Bogdanovic's injury-time penalty gave Barnsley a last-gasp win and sent them through to the Carling Cup third round for the first time in eight years. Rob Kozluk's 90th-minute own goal had earlier cancelled out Bogdanovic's opener.
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