This was the first time Leicester had taken to the pitch in a league match without their talismanic striker since March last year. Vardy watched from an executive box as he serves the first of what could turn out to be a two-game suspension. Leicester coped admirably without him.
This emphatic victory means they need just five points from their final three matches - away to Manchester United, at home to Everton, away to Chelsea - to ensure they win the first league title in their 132-year history.
But it might not even come to that. Spurs were at home to West Bromwich Albion early today - a match they should win - but, trailing the leaders by eight points, Mauricio Pochettino's men have no margin for error as they desperately try to catch Claudio Ranieri's side.
"We play with our heart and it's difficult to beat those who play with their heart and soul," Ranieri said after the game.
It was after a late winning goal by Ulloa, in the last minute against Norwich City, in February that it emerged a seismometer installed in a school close to the stadium had detected "sudden energy release" - a quake with a magnitude of 0.3 - from City fans when the ball hit the net.
That win fuelled belief. It grabbed the attention of the rest of the league. There was even a social media account set up - @VardyQuake - to give updates of when the earth moved again. It more than likely shifted once more with Ulloa's last-minute penalty against West Ham, which earned a precious point eight days ago. He took his chances yesterday, too.
How would Leicester cope without Vardy? Would the Tinkerman tinker? Rightly, Ranieri decided not to. Too much variation would have led to doubt. Instead, Leicester retained their 4-4-2 formation, with Ulloa in for Vardy and Jeffrey Schlupp replacing Marc Albrighton, who has appeared tired of late. Both were outstanding.
It helped that Swansea self-destructed, conceding a comical goal after just 10 minutes to Riyad Mahrez, who has become the first African footballer to win England's PFA player of the year title.
There was then another blunder, Ulloa able to power a header in from a free kick.
Ulloa's second and a final one from Albrighton finished Swansea off. Cue another spike in that seismometer.
Sunderland crawled out of the relegation zone and Arsenal dropped points in their quest for a top-four finish in a lively 0-0 draw at the Stadium of Light.
The point lifts Sunderland into 17th, ahead of Norwich City on goal difference. Arsenal stayed fourth, five points above Manchester United, who have a game in hand.
Telegraph Group
