Callum Hudson-Odoi scored one of Chelsea's three goals in what could be his final appearance with the team.
The force - of VAR - was with Chelsea against struggling second-tier Sheffield Wednesday.
Chelsea conceded a first-half penalty, which the video assistant referee subsequently overturned, and quickly got a penalty of its own, which VAR confirmed.
Callum Hudson-Odoi scored on what could be his final Chelsea appearance and Willian netted twice at Stamford Bridge.
Hudson-Odoi started despite reportedly submitting a transfer request in an effort to force through a move to Bayern Munich ahead of Thursday's transfer deadline, and the 18-year-old winger netted Chelsea's second goal after 64 minutes.
Sheffield Wednesday had a penalty overturned by VAR after 22 minutes and Chelsea had a spot-kick awarded four minutes later, Willian converting from the spot, after referee Andre Marriner's decision had been confirmed by VAR.
''With VAR, it was obviously the correct decision but I thought we should have had a corner as a result (instead of a dropped ball) so that seemed a strange decision. But we're all a bit wiser now,'' Owls caretaker boss Steve Agnew said.
Chelsea celebrated its first goal in front of the Shed End, packed with visiting fans, some of whom took exception, with missiles thrown.
''I wasn't aware of that. It's not the right thing to do,'' said Agnew.
Willian added a late third as the Blues advanced to the fifth round.
Gonzalo Higuain made his first appearance as Chelsea made eight changes following its win over Tottenham.
Higuain made his debut after signing late on Wednesday on loan from Juventus.