Barnsley took the points in the latest U23s game, as a strong first half display was enough to secure victory.
The Tykes raced into a 3-0 first half lead and, despite an improved second half display, the U's were unable to get back into the match.
The U's hopes were hit early on with an injury to Louis Dunne, with Tariq Issa coming on in his place.
Barnes pulled off a fantastic low stop to deny Fielding's powerful header, but the Barnsley man did get his goal on 34 minutes.
A long free kick was lofted into the box and Fielding was on hand to toe poke past the U's keeper.
They then got their third five minutes later. A goalmouth scramble ended with Chris Sang poking home despite the best efforts of Percy Kiangebeni.
Three down at the break, the U's replaced Taymar Fleary with David Agboola.
But he could do little about Barnsley's fourth as they cut a corner kick back to the edge of the box and Fielding volleyed home a low effort that nestled in the back of the net.
The U's knew they faced an uphill task at this stage, but kept on going and had the better of the final quarter of the match.
Tykes stopper Jake Greatorex pulled off a good stop to turn away Noah Chilvers' effort and the U's number four went close again with a drilled shot that went inches wide on 71 minutes.
And Issa almost grabbed a consolation at the end, but his whipped effort went just past the far post.
U's: Barnes, Scott, Clampin, Chilvers, Kensdale, Kiangebeni, Miller, Dunne (Issa 9), Jones, Hutchinson, Fleary (Agboola 46)
Subs not used: Coulter, Ager, Hyde