The visitors introduced Andre Ayew, Luciano Narsingh and Tammy Abraham as they chased the game and Carvalhal said that left Swans open to the counter-attack.
Glenn Murray opened the scoring from the penalty spot and Carvalhal made his first change when he sent on forward Ayew for winger Nathan Dyer after just 36 minutes.
Narsingh then went on for defender Mike van der Hoorn at half-time as Swansea went 4-4-2 from 3-5-2 and then striker Abraham was sent on for midfielder Tom Carroll after 66 minutes with the Swans still trailing 1-0.
Further goals from Murray and Anthony Knockaert put Brighton 3-0 up, before Abraham got a goal back five minutes from time when his shot deflected in off Lewis Dunk.
There was still time for Jurgen Locadia to add a fourth for Albion and Carvalal admitted his gamble did not come off.
Carvalhal said: "Brighton won and deserved to win. We did a big bet today and we lost that bet.
"We gambled and lost the gamble but we don't lose our abilities and quality and we will be super sure to be on a good level in the next game in the Premier League on Saturday.
"We made mistakes we usually don't do.
"In the period we controlled more of the ball, we played offensive and after we were losing 1-0, I was thinking we must change things because I wasn't happy.
"We put Andre Ayew on in attack. We took some risks and put Luciano on the wing and played with Andrew Ayew and Jordan (up front).
"In that period, we did well and almost scored twice. One of the situations with Luciano and another sitiuation with Ki that the goalkeeper made a fantastic save, which could have made it 1-1.
"We took all the risks because we are not happy to lose and wanted to do things to try to win.
"We did a high press in that moment. So when you do a high press, you can win a lot of money or you can lose all the money.
"We put Tammy on the pitch when the game was 1-0 and we took one midfielder off the pitch. We knew in that moment the risk because we were playing with Tammy, Jordan, Andre and Luciano.
"If we score one goal, we change things and can win the game but we knew also if they score the second, it would be very difficult for us, like it happened.
"If I was to critic myself, the risk we took with Tammy probably we can wait a little more, the last ten minutes. You take decisions as a manager and in that moment, if you take all the risks, we score and we win the game, the manager is a genius.
"If it doesnt happen as we want, that is football. But we took all the risks and we tried everything to win."
Keep up with all the top football news and transfer gossip from England, Scotland and beyond with footballwire.co.uk