Whisper it quietly, but a beast might be stirring at Flushing Meadows.

Milos Raonic is the sleeper of the US Open. Touted as a leading member of Generation Next in men's tennis, the powerful 22-year-old Canadian roared into the fourth round on Saturday with a 6-7 (4), 6-4, 6-3, 6-4 win over Spain's Feliciano Lopez.

Raonic's thunderous serve has landed him a chart-topping 65 aces for the tournament. His heaviest delivery of 145 miles per hour (72.4 kph) is the fastest at the event.