Rank outsider Christian Harrison upset top seed Cristian Garin of Chile in the second round of the Delray Beach Open on Saturday.

Harrison, 26, ranked No.789, has been hampered with injury and a number of surgeries, but won 7-6 (7-3) 6-2 to reach his maiden tour quarter-final.

“I just love the sport, I love what I’m doing,” Harrison said.

“I just can’t wait to keep playing and hopefully have a good, healthy next couple of years.”

Garin, who had a first-round bye, had no answer to Harrison’ style.

“He played really flat, really fast. I hope he can play like this the rest of the year,” Garin said.

Harrison will play Gianluca Mager of Italy next. Mager beat sixth-seeded Sam Querrey 7-6 (8-6) 6-1.

Second-seeded John Isner was never troubled in his 6-4 7-6 (7-4) win over Brazil’s Thiago Monteiro.

The big-serving American will next face Sebastian Korda, who battled to beat fifth-seed Tommy Paul 4-6 6-3 6-2.