Whatever Paul Clement said to his players at half time sparked an unbelievable change in energy, as the home side looked a completely different team.
Abraham finished from close range after 56 minutes to cancel out Gray's first Watford goal, but Richarlison brushed aside Alfie Mawson's timid challenge in the final minute to finish off the underside of the crossbar.
Dutch defender Mike van der Hoorn made way for striker Tammy Abraham, whilst Roque Mesa replaced Sam Clucas in midfield. "And I think I did the right thing to make the changes at half-time in terms of the shape and personnel".
Swansea were struggling for possession and also to make the ball stick when they played it into Bony's feet. "The second half we were much better but overall it was a 90-minute game where we played for 40 minutes", Clement told Sky Sports after the match.
But Richarlison exploited some brittle defending to power in a late victor and give Watford a first league win at Swansea since February 1983.
"I changed the system at half-time - I had to do it - and we took control of the game and continued to threaten after getting a good goal".
"That's not enough. I am very disappointed for the supporters because they have come here three times this season and we have lost every game".
"He's a very good player and we've got good players who are on the bench, and I've told them I'm not going to be anxious who's upset if they're not in the 11 or the 18 I have to pick".
"That's not good enough".
"It's supposed to be easier at home, but for some reason it's not at the moment".
The 35-year-old is a club legend having played for the Swans in all four divisions of the English Football League, and he played an important role in helping the team avoid relegation from the Premier League last season. The crowd were disappointed at the end of the first half and I could understand that because I was the same.
Watford head coach Marco Silva was delighted with the way his side bounced back from a tough start to the second-half to claim all three points at Swansea.
"Our team showed that they had forgotten what happened last Saturday, which was very important".
"We wanted three really important points and we've got our third win away in the Premier League, which is very hard for a team like Watford".
"But we needed to believe we could score the second to kill the match".
Swansea's dismal start to the season continues, despite dominating for most of the second half.