Sunderland defender Peter Hartley and striker David Dowson have extended their Chesterfield loan spells until the end of the season.
The 19-year-olds, who both signed professional contracts with the Black Cats in 2007, joined the Spireites on initial one-month deals.
They have since proved a success - Dowson scored within four minutes of his Chesterfield debut against Brentford, while Hartley has turned in combative performances at the back.
Spireites manager Lee Richardson told the club's official website: "We are pleased that the two Sunderland lads are staying with us some more as they continue to provide healthy competition in the squad. This helps keep everyone on their toes."
Rotherham's 10-point deduction has allowed the Spireites to move into the final play-off spot, though they are 16 points off automatic promotion.