The Nigeria striker Isaac Success scored as Watford buzz through Berkshire to maintain their perfect record.
Success opened the scoring for Watford in the first half.
Summer signing Quina, 18, confirmed victory for Javi Gracia’s side after Isaac Success had put the visitors ahead and heaped more misery on Paul Clement’s Reading.
It was only the second goal 22-year-old Success has scored since signing for a club-record £12.5million from Granada in 2016.
A physical presence up front, Watford recognised the aerial threat Success possesses and the vulnerability of Reading’s defence.
The Nigerian striker sent one header whistling past Walker’s crossbar, closely followed by Chalobah just missing.
Gracia’s men head back to the Vic joint top of the Prem and into the next round of the Cup. They’re buzzing.