Madrid - Nick Kyrgios could face Rafael Nadal in a blockbuster third-round clash at the Madrid Masters on Thursday after easily seeing off Ryan Harrison 6-3, 6-3.
Nadal begins his quest for a fifth title in Madrid later on Wednesday against Italy's Fabio Fognini.
Kyrgios and Nadal have only met twice with the Australian making his breakthrough with a four-set win over the 14-time Grand Slam champion at Wimbledon in 2014.
Nadal, though, edged their only previous meeting on clay at the Rome Masters last year.
Fifth seed Milos Raonic is also into the last 16 as he got the better of a battle between two big servers 6-4, 6-4 over Gilles Muller.
Raonic will face Belgium's David Goffin next.
David Ferrer made it into round three without having to hit a ball as Jo-Wilfried Tsonga withdrew with a shoulder injury.
World number two Novak Djokovic begins life without long-term coach Marian Vajda later against Nicolas Almagro.
Results from the ATP Madrid Masters/WTA Madrid Open on Wednesday (x denotes seeding):
Milos Raonic (CAN x5) bt Gilles Muller (LUX) 6-4, 6-4
Nick Kyrgios (AUS x16) bt Ryan Harrison (USA) 6-3, 6-3
David Ferrer (ESP) bt Jo-Wilfried Tsonga (FRA x10) - injury walkover
Anastasija Sevastova (LAT) bt Lara Arruabarrena (ESP) 7-5, 6-2