Both sides were then reduced to ten men midway through the half when Alex Bruce and Stephen Bywater stupidly scuffled at a corner, before squaring up again as they walked off.
Despite being behind, Ipswich had by far the bulk of the possession and chances and deservedly levelled on 70 minutes with a poacher's strike from former England forward Francis Jeffers.
The hosts kept pushing forward and won the game with a minute to go when former Ipswich loanee Jay McEveley brought down sub Danny Haynes, who picked himself up to slot home the penalty.
Jeffers shot wide early for Ipswich before Steve Howard was denied an 18th goal of the season by an offside flag after bulleting home a header from a David Jones free-kick.
Jeffers was inches wide from 20 yards before Oakley fired home a 25-yard volley after Howard flicked on a long punt from Bywater.
Bywater denied a low Jon Walters shot and Jeffers headed over from a Jaime Peters cross, before the double sending-off as Bruce and Bywater placed their foreheads together at a 28th minute corner.
Ipswich piled on the pressure as half-time approached and Owen Garvan twice fired inches wide of the far post, the second time with Jeffers fractionally away from touching the ball home.
Ipswich continued to look the more likely in the second half, and five minutes in Jeffers hit the top of the bar from 25 yards with sub keeper Lee Grant nowhere.
Shane Supple saved a curling 30-yard Jones free-kick - only Derby's second attempt on target - before Jeffers latched on to a long clearance from Fabian Wilnis to tuck the ball home.
Both sides went for the win in the final 20 minutes in scorching sunshine at Portman Road, but it was Ipswich who prevailed when Haynes was nudged over by McEveley and the striker coolly slotted the penalty past Grant's left-hand, although the keeper went the right way.
Ipswich now go into next Sunday's East Anglian derby at Norwich looking for a double over their arch rivals, while Derby must regroup for a huge game at home to relegation-bound Luton.
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