Webster headed in from Pascal Gross’ corner in the 63rd minute to make it 3-0 before O’Mahony added a fourth with a powerful shot from the edge of the box two minutes later.
Roles was then shown a straight red card for a foul on substitute Kacper Lopata in the 89th minute as Brighton cruised to victory.
Despite the win, Hurzeler was left frustrated by the injury to O’Riley, calling the tackle “ridiculous” and questioning why it went unpunished.
Brighton will now await the results of O’Riley’s scan to determine the extent of his injury as they prepare for their next Premier League match against Brentford.