Claudio Ranieri’s leaders looked destined for a damaging defeat at the King Power Stadium after late goals from Andy Carroll and Aaron Cresswell put the Hammers ahead following Vardy’s dismissal for diving.
Referee Jonathan Moss’s decision to give Vardy, who had opened the scoring in the first half, a second booking incensed the Leicester fans and they were even more irate when he awarded West Ham the penalty that Carroll converted to equalise.
But with just seconds remaining, Moss made another crucial decision and this time it went Leicester’s way as he gave a soft penalty that substitute Ulloa drilled home to leave the Foxes eight points clear of second placed Tottenham.
It summed up the astonishing nature of the finale that Moss was still booed off despite his late gift to Leicester, whose lead at the top will be cut to five points with four games remaining if Tottenham win at Stoke on Monday.
Vardy’s suspension next week against Swansea just adds another twist to an incredible title race.
Right from the opening minutes it was clear Leicester’s astonishing march towards the title was about to become even more enthralling.
When Cheikhou Kouyate met Dimitri Payet’s free-kick with a powerful header, a goal seemed certain, yet Kasper Schmeichel somehow got a fingertip on the ball to push it onto a post.
It then bounced along the goal-line before rebounding off the other post and back in the grateful arms of the Leicester goalkeeper.
If Liverpool manager Jurgen Klopp has patented his brand of ‘heavy metal’ football, then it can’t be long before Leicester’s frenzied approach, undoubtedly effective but at times as subtle as hardcore techno, gets a label of its own.
Thundering into tackles and moving the ball at breakneck speed, Leicester embarked on a blistering counter to take the lead in the 18th minute.
Schmeichel caught the ball from a West Ham attack and within seconds had launched a throw out to Riyad Mahrez on the right flank.
Mahrez quickly shifted possession onto N’Golo Kante and, with West Ham left hopelessly out of position by the speed of the break, the France midfielder measured a pass to Vardy, who took one touch just inside the penalty area before driving into the far corner for his 22nd league goal .
But for virtually the first time all season, Leicester’s fortunes took a turn for the worse in the 56th minute when Vardy chased a through-ball into the penalty area and appeared to deliberately nudge his legs into Angelo Ogbonna before throwing himself to the turf in pursuit of a penalty.
Moss saw it as a dive and gave Vardy a second booking to the disbelief of the forward.
It will take some time to take that all in, but here's a breathless second half in 10 images [2-2] ⚒ #WHUFC #LEIWHU pic.twitter.com/IQ4EZ4LQji
— West Ham United FC (@whufc_official) April 17, 2016
Suddenly, there was a genuine sense of anxiety in the stands as Ranieri’s men were penned deep inside their own half.
They seemed to have weathered the storm until the 83rd minute when Moss once again took centre stage.
As they contested a corner, captain Wes Morgan needlessly bundled over Winston Reid and Moss pointed to the spot for a penalty that substitute Carroll crashed by Schmeichel.
If they were nervous before that, there was no mistaking the panic as Leicester were confronted by a serious test of their mettle and they cracked in the 86th minute.
Michail Antonio was allowed to get to the byline and deliver a cross that was only partially cleared to Cresswell, who had been left unmarked to bend a sublime strike into the top corner.
Several of Ranieri’s players fell to their knees, with Danny Simpson burying his head in frustration, but the drama wasn’t over.
After spending the afternoon as public enemy number one to the Leicester fans, Moss atoned for his perceived mistakes in stoppage-time when he awarded a soft penalty for Carroll’s challenge on Jeffrey Schlupp and Ulloa held his nerve to rifle home the spot-kick.
