It marked the Toon's eighth consecutive Premier League defeat and they ended with nine men.
Ulloa headed the Foxes ahead after 38 seconds and it was 2-0 within 17 minutes as Wes Morgan poked home.
Janmaat was shown a second yellow card for fouling Jamie Vardy in injury time. Before then, Williamson was also sent off for a second yellow card on the hour mark after a similar foul on Vardy.
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