Theo Walcott and Granit Xhaka were the other two scorers who confirmed a convincing win for the Gunners. Arsenal are placed in the third position in the league table with 10 points from 5 matches.
Sanchez started the proceeding by scoring the opening goal in the 17th minute from Alex Iwobi's pass. Hull City's Jake Livermore was sent-off minutes before half-time after he handled the ball deliberately inside the penalty box. Sanchez took the resultant penalty but his effort was saved.
Theo Wacott increased the lead in the 55th minute after Alex Iwobi backheeled a pass to the English player. Walcott found the back of the net with ease.
The home side pulled on back after Petr Cech fouled Hull's Dieumerci Mbokani inside the box. Robert Snodgrass scored the goal from the penalty spot.
Just when it seemed that Hull were trying their best to fight back, Chilean Sanchez completed his brace and scored team's third goal.
Substitute Granit Xhaka hammered the final nail in Hull's coffin with stunning 30 yards striker in the dying moments of the match.
It was a sensational win for the Gunners who move up the tabel to third position with 10 points behind Everton and table toppers Manchester City.