American qualifier in huge ATP Tour upset

American qualifier Christian Harrison upset top seed Cristian Garin of Chile in the second round of the Delray Beach Open.

Harrison, ranked No.789, prevailed 7-6 (7-3) 6-2 to double his career wins on the ATP Tour to four and reach his maiden top-tier quarter-final.

The 26-year-old - whose career has been hampered by multiple surgeries - squandered three consecutive set points serving at 6-5 in the first set and lost serve, but regrouped to dominate the tiebreaker.

He swept the final four games of the match to become the second-lowest-ranked quarter-finalist in tournament history.

"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."

Former world No.3 Juan Martin del Potro was ranked No.1042 when he reached the quarters in 2016, on his caomeback from injury.

Garin, who had a first-round bye, had no answer to Harrison in the cool afternoon playing conditions.

"These conditions are good for him," Garin said.

"He played really flat, really fast. I hope he can play like this the rest of the year."

Harrison next plays Gianluca Mager of Italy, who advanced by beating sixth-seeded and 2016 champion Sam Querrey 7-6 (8-6) 6-1.

Second-seeded John Isner hit 22 aces and never faced a break point in his 6-4 7-6 (7-4) win over Brazil's Thiago Monteiro.

The big-serving American will next face Sebastian Korda, who rallied to win an all-American match against fifth-seeded Tommy Paul 4-6 6-3 6-2.\ep playing and hopefully have a good, healthy next couple of years."