Flick through our gallery to relive the key moments from Adams Park where the Black Cats salvaged a point from the League One fixture.
Alex Samuel put the visitors ahead 10 minutes before half-time.
With tensions running high, substitute Jack Baldwin was shown a yellow card for running on the pitch and kicking the ball away.
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After an extended delay while Wycombe goalkeeper Ryan Allsop received treatment, Flanagan was also booked after a minor scuffle
Flanagan then took a kick from Wycombe striker Samuel and was forced off with the help of the physio.
Jack Ross and assistant James Fowler remonstrated with the fourth official after they felt more time should have been added on. Fowler was booked as a consequence.
Watmore was quickest to react after a fumble from Allsop and fired Sunderland level in stoppage-time.
It was Watmore's first league goal the season.
Precisely what happened is not quite clear, but it appeared but it appeared members of the Sunderland bench, including George Honeyman and kitman John Cooke, tried to retrieve a loose ball.
Wycombe assistant manager Richard Dobson got their first, the ball disappearing and a confrontation ensued.
Sunderland captain George Honeyman and Nathan Tyson of Wycombe are both sent off after the brawl.
Honeyman will now serve a three-game ban and miss the Checkatrade Trophy final.
The Wycombe midfielder also saw red for an awful challenge on Watmore which left the forward in agony.
"I am going to speak to the referee and get clarity on it. Then I can look at everything and see if it was justified."
"The ball has come into our technical area and Dobbo has gone to volley it back into play. The ball then went missing and both benches erupted. I was doing my best to stop my players getting involved."