Bent, who is on loan from Aston Villa, opened his Derby account at the weekend in an FA Cup fourth-round victory over Chesterfield.
And he proved the match-winner against Blackburn, scoring two second-half goals to send Derby level on points with leaders Bournemouth.
Blackburn fell behind in the 68th minute when a long throw from Ryan Shotton was flicked on for Bent to convert, and the former England striker found the net again in stoppage time after Chris Martin's initial effort had been saved.
Elsewhere in the Championship, Rotherham United pulled five points clear of the relegation zone with a 4-2 home victory against Bolton Wanderers.
Rotherham led 4-0 after 57 minutes, but goals from Liam Trotter and Matt Mills salvaged some pride for Bolton.
Millwall overcame the 45th-minute dismissal of teenage defender Sid Nelson to earn a 0-0 draw against Reading, while the game between Sheffield Wednesday and Birmingham City also finished goalless.
MK Dons missed out on the chance to go top of League One, a 1-1 draw at Scunthorpe United leaving them two points behind Swindon Town and Bristol City.
Chesterfield are fifth after responding to their FA Cup exit at the hands of Derby with a routine 3-0 win over Crawley Town, the third-tier's bottom club.
Dagenham and Redbridge came from behind to draw 1-1 at Cambridge United, who held Manchester United on Friday, and climb out of the League Two relegation zone, while Bury won 1-0 at Accrington Stanley.
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