© PA Photos
The incident occurred in the 78th minute when a ball boy, standing behind the Swans' area, appeared to take time in returning the ball to play. Hazard approached the youth and grappled the boy as he fell to the ground clutching the ball.
Hazard then attempted to kick the ball out from underneath the boy, who was left clutching his ribs in pain.
The sending-off left Chelsea with 10 men and 10 minutes remaining to overturn a 2-0 aggregate deficit.
Minutes later a Tweet on the official Chelsea account read: "Has football gone mad? Hazard is sent off for kicking the ball under a ball boy attempting to smother the ball rather than return it. #CFC"