FA Cup holders Leicester City made an impressive start to their defence of the trophy as the much-changed Foxes swept aside fellow shadow side Watford.
Youri Tielemans - who scored City's winner at Wembley last May - put them ahead from the spot after Francisco Sierralta fouled Jannik Vestergaard.
James Maddison's cool finish doubled the lead but Joao Pedro immediately pulled one back for the Hornets.
However, strikes from Harvey Barnes and Marc Albrighton sealed an emphatic win.
The sides made 16 changes between them - Leicester nine and Watford seven - from their previous Premier League games, with the majority enforced by injury or Africa Cup of Nations duty.