The Toffees played for the first time since being given a ten-point deduction by the Premier League for breaching financial rules, but were beaten 3-0 by the visitors.
Ahead of kick-off, a video on X showed one fan spotting seven-time Premier League winner Keane on punditry duties for Sky Sports in the TV studio.
The former United captain saw the camera being pointed in his direction and appeared to angrily tell them to focus on their own club instead of him.
Keane's co-pundit Karen Carney was seen just behind him watching on, with Michael Dawson turning around towards the end of the clip.
Eventually, the players made their way from the tunnel and Everton fans, some of whom marched in protest to the stadium prior to kick-off, booed the Premier League anthem as they continued to voice their displeasure.
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However, the action on the pitch wasn't much better for them as it took just three minutes for United to open the scoring.
A stunning overhead kick from Alejandro Garnacho put the visitors in front, with Everton fans left angered yet also in awe of the strike.
Sean Dyche's side had chances to equalise before the break but they were made to pay for their missed attempts as United took control.
Marcus Rashford doubled their lead from the penalty spot with his second goal of the season before Anthony Martial added a third.
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Roy Keane slams Erik ten Hag for 'absolute rubbish' praise of Bruno Fernandes
Back in the Sky Sports studio, Keane suggested United showed glimpses of swagger returning after a mixed start to the season.
However, he went on to slam Erik ten Hag's praise of captain Bruno Fernandes after he handed the penalty-taking duty to Rashford.
Despite their shortcomings this season, United's victory at Everton was their fourth in their last five matches in the Premier League.