Swansea boss Paul Clement hailed the development of Alfie Mawson after the defender helped secure Carabao Cup success at Reading.
Former England Under-21 centre-back Mawson swept home from a corner early in the second half at a sparsely-populated Madejski Stadium before substitute Jordan Ayew wrapped up a 2-0 third-round win late on.
Twenty-three-year-old Mawson has played in all of the Swans' seven games so far this season and his contribution to their four clean sheets has delighted his manager.
Premier League Swansea, who won this competition in 2013, made seven changes for the clash in Berkshire, while their Championship opponents made nine.
The Royals more than held their own in an uninspiring first half but, once they fell behind, Jaap Stam's side had little answer to the superior quality of their visitors.
Clement conceded his players had been unable to assert the authority in the opening period.
Reading manager Stam was frustrated by the part played by referee Andy Davies in Swansea's second goal.
The ball rebounded off the official in the middle of the field, allowing Ayew to race away and end the tie with a firm strike into the bottom right corner.
"In the majority of the game we dominated, the first half we dominated, second half as well," said Dutchman Stam.
"But you concede two easy goals; one by a set-piece - which never can happen basically - the second one by the referee making a one-two with one of their players.
"Mainly it kills the game because then it's 2-0 and then it's easy.
"You saw their reaction as well when they scored the second one, they were very happy because the pressure is off and it's just sitting and waiting and holding back, and maybe they can score a third one."