Town stormed to fourth in the table with a 3-2 win at Cardiff City. Tommy Miller put the Blues ahead from the spot before Georges Santos netted his first for Town. An Earnshaw penalty pulled one back but Chris Bart-Williams added a third. A late Peter Thorne goal was not enough for the Bluebirds.
Town lined up unchanged from last week's 3-0 win at home to Sheffield United, Georges Santos recovering from his bruised foot.
Former Blue Gary Croft was booed by his old fans in the opening stages of the game, a period of few chances at either end.
Town gradually took control of the game and Richard Naylor wasn't far from a goal with a header that went just over in the 10th minute.
Cardiff's first tester for Kelvin Davis was a clearance from halfway by Richard Langley, which the Town keeper saw by his post.
The Blues were passing the ball around sublimely with the home players chasing shadows. In the danger area Jermaine Wright had a shot blocked before Jim Magilton had an effort deflected wide from a fine run from Matt Richards. Soon after Shefki Kuqi shot over.
Former Palace man Julian Gray found himself in the book on 20 for a late and crude tackle on Jim Magilton, which left the Town skipper needing treatment. Eventually the Town captain limped off with what looked like an ankle problem and must be a doubt for Wednesday's trip to Nottingham Forest.
Tommy Miller replaced the Northern Irishman and was immediately into the action, playing in Ian Westlake on the left, inside the Cardiff box. As the youngster broke into the area he was felled by Gary Croft, the referee having little doubt it was a penalty. Miller took the kick and beat Neil Alexander to his left.
The lead was all Town deserved for probably their best first half away from home this season. Other than Langley's distance effort, Town's only moment of danger came when Earnshaw failed to connect with a low ball across the box.
On the half hour Kuqi had a shot blocked but not long after the Blues were further in front. Ian Westlake sent over a corner from the left and Georges Santos volleyed it home at the far post, his first goal for Town.
On 35 Richard Langley received a caution for a two-footed challenge on Jermaine Wright and Chris Bart-Williams picked up his seventh yellow card of the season for a foul on the largely anonymous Rob Earnshaw.
Late in the half Peter Thorne headed wide from a corner, but it had been Town's half, the players applauded off by the large and noisy crowd standing on the terracing. England's rugby victory was proving a popular topic to sing about, while viewing the Blues in action was just like "watching Russia”.
No changes at the break and initially the game took on the same pattern as the first half. Kuqi almost played in Darren Bent from the left. Soon after the young striker had the ball in the net, however when in an offside position.
On 49 Gary Croft felled Westlake on the edge of the area and picked up a yellow card. Croft and his driving antics also provided amusement for the Town fans as did his post-prison surveillance tag. Matt Richards put the freekick into the wall.
There was controversy in the 56th minute when Cardiff were awarded a penalty. Few can have been certain what the kick was awarded for, although Cardiff's Australian centre-half Tony Vidmar had gone to ground.
The Town players argued but to no avail and Rob Earnshaw beat Kelvin Davis from the spot for his 100th Bluebirds goal.
Earnshaw's goal gave the home side new impetus and they had far more of the ball than they had in the first half. On 66 John Robinson picked up a yellow card for arguing with a linesman.
Kelvin Davis saved Richard Langley's shot in the 70th minute before Earnshaw went high and wide after Fabian Wilnis had lost possession not far outside the Town area.
A minute later Shefki Kuqi took the ball down with his chest and lashed the ball straight at Alexander who might have been in trouble had the ball not gone straight to him.
Peter Thorne came close to putting the ball in the Town net in the 72nd minute, Kelvin Davis brilliantly tipping his header over the bar. However, a flag had already been raised and a goal would not have counted.
Davis saved more comfortably from the out of sorts Earnshaw, Cardiff largely misfiring when close to goal.
On 82 Chris Bart-Williams added the Town third and the second of his loan spell at Portman Road. Westlake's corner from the right was half-cleared to the edge of the area where the Charlton man picked the ball up, turned inside a defender and fired into the top corner.
Nerves on the Town terrace disappeared momentarily until poor marking at a corner allowed Thorne to head home Cardiff's second.
With the game moving into injury time Richard Naylor did well to clear ahead of Kelvin Davis and John Robinson, both players requiring treatment before carrying on.
There was just time for referee Andy Hall to show a yellow card to Vidmar for a foul on the again impressive Westlake before he blew the final whistle.
A superb first half display set up the Town win with a bigger lead probably deserved at the break. The penalty was very much against the run of play and extremely harsh, no one seeming entirely sure why it was awarded.
The home side showed more after their first goal but Town were rarely under any serious pressure, despite a tense finish.
Santos was a rock at the back while Westlake continues to shine. Kuqi and Bent were always threats up front while Bart-Williams was as unflustered as ever in the centre of midfield.
Town: Davis, Wilnis, Richards, Santos, Naylor, Magilton (Miller 26), Bart-Williams, Wright, Westlake, Bent, Kuqi.