Substitute Shane Long salvaged a point with a close-range header as Derby defended desperately following the sending-off of centre-half Andrew Davies for two yellow cards 19 minutes from the end.
Midfielder Seth Johnson had scored his first goals since his return to the club to give Derby a chance of becoming only the second Championship side to beat Reading this season, but Steve Coppell's team showed why they are the runaway leaders.
Although they were well below their best, Reading were easily the superior side in the second half and Long's late equaliser made the final scoreline a fair one.
Derby could not be faulted for effort and commitment but will look back on chances lost after Johnson twice put them in front.
His first in the 32nd minute was set up by Tommy Smith, whose low cross from the right wrongfooted two Reading defenders to leave Johnson with an easy finish from just outside the six-yard area.
But Derby held the lead for less than two minutes as Glen Little cleverly chipped the ball in from the Derby right and Kevin Doyle glanced a header into the top right-hand corner.
Reading moved up a gear after the break and it was a surprise when Derby regained the lead in the 62nd minute.
Johnson struck the ball low with his right foot from 20 yards to beat Marcus Hahnemann inside his left-hand post.
But the home side then lost Davies who recklessly dived in and caught Long leaving the referee with no option but to produce a second yellow card.
It looked as if Derby might survive that as they managed to hold Reading at arms length until two minutes from the end. Nicky Shorey floated a corner to the back post where Steven Sidwell headed it back across goal and Long rose above at least two defenders to head past Lee Camp.
Although Reading were unable to find another goal which would have given them 11 straight league wins, they remain unbeaten in the Championship since the opening day of the season and Derby can take heart from a battling performance against the leaders.