Kelechi Iheanacho rifled the opener past Petr Cech after poor defending from the visitors, who had 20-year-old defender Konstantinos Mavropanos sent off 92 seconds later for hauling down the forward as he broke through on goal.
Leicester earned a first Premier League win over Arsenal since 1994 as Arsene Wenger’s penultimate game in charge of the Gunners ended in another away defeat.
Arsenal levelled through Pierre-Emerick Aubameyang, but Jamie Vardy’s penalty, awarded after Henrikh Mkhitaryan brought down Demarai Gray, and Riyad Mahrez’s late breakaway goal sealed the victory for the hosts.
Arsenal remains the only side without an away point in English league football in 2018, while victory for the Foxes means they could still overhaul Everton for eighth place with victory over Tottenham on the final day.
Vardy’s penalty means he has now scored six goals in his last six Premier League games against the Gunners, who have lost seven consecutive top-flight away matches for the first time since 1966.
In the final minutes, Arsenal fans chanted Wenger’s name and were joined by the home supporters, many of whom stood to applaud the Frenchman.
Source: BBC News