Watford head coach Xisco Munoz called for calm after Adam Masina's last-gasp free-kick secured a 2-1 win at Cardiff and sparked wild celebrations.
The late winner propelled the Hornets into the Championship automatic-promotion places and ended Mick McCarthy's unbeaten run as Bluebirds manager.
Watford defender Sierralta gave his side a mountain to climb in the 14th minute after prodding home an own goal from Josh Murphy's cross.
But captain Nathaniel Chalobah levelled a minute later with a sublime solo strike.
That gave Masina the opportunity to drive the ball towards the centre of the goal, and Cardiff goalkeeper Dillon Phillips could not stop the ball from hitting the back of the net to create wild celebrations on the Watford bench.
"The emotion was top on the pitch but now we need calm," said Xisco. "It is a very important three points from a very important game.
"It was an important game because we played against a very good team, a tough team who were fully fit and 11 games without defeat.
"The team controlled the game and had very good chances and I'm proud of the players and the performance.
"We must have humility and our feet must stay on the ground. If we can continue to work with the same ambition, then we will see if we can complete our objective.
"We need to give our best in all the games, we have time for recovery and have good momentum, the most important thing is we need to deliver another performance.
"We knew we were playing warriors today. They have very good players with intensity and are very dangerous at set-pieces so we had to be fully focused at all times.
"We were brilliant, it is difficult to stop those situations away from home, but we had more possession, control and clear-cut chances."
Cardiff muscled their way into play-off contention during McCarthy's stunning start to life in charge but are now seven points adrift of the top six.
But McCarthy, who had just received February's manager of the month award, was left fuming with the Watford players and staff after the heated exchanges at the end of the match.
"There was a guy who got booked for fouling Aden Flint in the box. He just ran and screamed in his face and ran off like a big coward," he said.
"Maybe if you go and push Flinty you should stand up and see the recriminations.
"I'm glad he didn't! Because Flinty might have boxed him one and he would have had a red card.
"Listen, I understand their celebrations at the end of the game, but I do think it's good to be magnanimous in victory as well. And it's a lot easier to be magnanimous in victory.
"As disappointed as we are, you understand how elated they are.
"It was very cruel and tough for the lads having worked so hard to keep a good team at bay for a good while. I thought the lads acquitted themselves very well.
"Then just at the very end they get the free-kick and poor old Dillon's wondering how it happened.
"He did hit it particularly well. It's just one of those things that happens so I won't be too hard on Dillon, that's for sure.
"Dillon's saying he should have saved it. If he's saying that then I'm not going to disagree with him, but he did hit it well.
"He saved two penalties a few weeks ago and we were all patting him on the back. I've no recriminations with him whatsoever."