Two first half goals from Jordan Evans and Callum O’Dowda sandwiched a Wes Fogden strike before Oxford added to their tally just before the hour mark when Chris Maguire scored.
Manager Darren Way made three changes from the side that beat Stevenage in the FA Cup on Saturday. Ryan Bird, Shaun Jeffers and Ryan Dickson dropped to the bench to be replaced by Ben Tozer, Wes Fogden and Francois Zoko.
The Glovers found themselves a goal down after just four minutes when debutant Evans picked up the loose ball 40 yards from goal after a misplaced pass in the Town midfield. The youngster unleashed an unstoppable shot that sailed past the diving Weale and into the net.
On 25 minutes the recalled Zoko jinked his way past two Oxford defenders only for his goal bound shot to be blocked by the back tracking defender.
With Town growing more and more into the game they levelled the scores on 37 minutes after a patient build up and some neat passing involving a number of players. The ball fell to Tozer just outside the box and the former Northampton man saw Fogden in space and played a neat through ball, which Fogden fired home past Slocombe from just inside the area.
Town were only level for five minutes as the home side went ahead through O’Dowda. A cross from the left wing from Josh Ruffels went over everyone in the Town area to land at the feet of O’Dowda, who controlled well to slam the ball past Weale.
Five minutes into the second half the home side had a strong penalty claim turned away by referee Stroud. Chris Maguire got past his marker and looked set to round Weale, but seemed to be bundled over in the area. Despite the shouts for a penalty referee Stroud waved play on.
Just moments later Maguire did score to make it 3-1 to the home side. The Scot picked the ball up 12 yards from goal and hammered the ball past Weale to score his first goal for Oxford.
Town pulled a goal back deep into injury through substitute Shaun Jeffers to make it 3-2, but the home side hung on to secure a place in the Area Final.
Town now face Barnet in League Two action at Huish Park on Saturday where Darren Way will be looking to turn Town's League form around.