The United frontman beat Lukasz Fabianski to a loose ball, prodding it ahead.
But Fabianski, realising his mistake, pulled back his arms.
Rashford nonetheless managed to dangle a leg and make contact with the Swansea keeper but was already on his way down with the ball well out of reach.
Neil Swarbrick waited and waited but then pointed to the spot, roared on by the Stretford End but leaving much of the viewing public back home stunned.
It was a dive, they chimed in near-universal agreement, with BT Sport pundit Graham Poll eventually admitting it should have been a yellow card for the England striker.
Here’s how Twitter reacted:
Chris Sutton sums it up: "Marcus Rashford dived."pic.twitter.com/Z3oxXfJa1G
— 101 Great Goals (@101greatgoals) April 30, 2017
No one on BT has used the word "dive" yet. This is why a lot of people think foreign players are treated differently to English players.
— Tony Barrett (@TonyBarrett) April 30, 2017
This is hilarious! @btsport pundits squirming in effort to defend Rashford. It was a dive! A good dive, but a dive nonetheless.
— Graham Ruthven (@grahamruthven) April 30, 2017
Rashford doing the full Jacques Cousteau for the pen though tough for ref to pick thru the sea of legs
— Kevin Garside (@GARSIDEK) April 30, 2017
Why do keepers keep doing that? Rashford on his way down before Fabianski gets there. Dive. #mufc
— Warren Haughton (@WarrenHaughton) April 30, 2017