On Monday, Ryan Harrison punched his ticket to the Houston second round after taking out 40-year-old Ivo Karlovic, 6-3, 6-4, at the US Men's Clay Court Championships in Texas.

"I felt like from the beginning I was in a good rhythm with my serve," Ryan said after his win. "I felt composed on the clay. I felt like I was moving well. Ivo can put you in some tough spots with some deep volleys because he's always serving and volleying and coming in."

26-year-old Harrison first played in this tournament 11 years ago, becoming the 10th player to win a  main tour match before his 16th birthday—he was 15 at the time. He lost to the then top-seeded James Blake in the following round.

"I remember that I was trying to play tennis," Harrison commented. "You know, I was talking about this tournament because the start of this year hasn't been the way I want to. And then whenever I'm coming back to a place with good memories, I love playing here in Texas. I live very close by. So to be back here, those memories are just really funny. I mean I have some vivid memories of that match that will never go away, I feel like as long as I live."

Playing in his favorite tournament, Harrison is hoping to turn his season around, having won just two main event matches thus far, scoring wins in the Australian Open and New York Open first-round matches. He is currently ranked No. 107, having dropped 45 spots since beginning of the year.

Karlovic, the 2007 champion, was last year's semifinalist, where he became the oldest player to reach the semifinals since Jimmy Connors in 1993—Karlovic had just turned 39 a month prior.

Up next for the American is either Henri Laaksonen or No. 6-seed Mackenzie McDonald.