The Gunners were not at their best as they struggled to get past a resurgent Hull side who surprisingly had more of the ball for majority of the game.
Sanchez opened the scoring with a controversial strike in the 34th-minute, with the ball appearing to have hit his hand before crossing the line.
Hull, however, were far from downhearted, and were quick to prey on an increasingly fragile-looking Arsenal backline, however for heroics of Cech, the visitor nearly levelled proceedings after Markovic’s cross found Niasse, whose shot was beaten away by the shot-stopper.
As clock ticked into added time, Arsenal cut the Tigers on the counter, with Mesut Ozil setting up Sanchez. His cross was headed goalwards by substitute Lucas Perez, striking the arm of Sam Clucas.
Advertisement
The defender was sent off for the foul and, and Sanchez wasted no time to slot home from the penalty to roll back the winning feeling among Arsenal supporters around the Emirates.
The Chilean has now scored 17 goals in 25 Premier League games this season; his best return in a PL campaign.
He becomes the first player to score 2+ goals in 3 consecutive Premier League appearances against the same team since Thierry Henry vs Charlton in 2002.
The Gunners move up to third, behind Tottenham on goal difference and nine points shy of Chelsea – a position they will retain if Manchester City fail to beat Bournemouth on Monday.