Newport - Eighth-seeded Donald Young knew what to expect from a player he's often practiced against.
That made it easier pulling off the upset over top-seeded Steve Johnson.
Young beat fellow American Johnson in the quarter-finals of the Hall of Fame Tennis Championships on Friday, 6-2, 6-3.
"I played well. Stevie, we know each other well and we train a lot in the off-season and practice throughout the year, so there's no mysteries there," the 26-year-old Young said. "I know how to beat him. You're going to have to play well, so I knew exactly what I had to do, and fortunately I was able to do it."
Young saved all five break points in the match.
The 26-year-old Johnson connected on just 46 percent of his first serves. Johnson is ranked a career-best 25th this week.
Johnson, who will be representing the United States at the Rio Olympics next month, is glad to see a friend doing well.
"It's great. I'm happy for him. DY is a great friend of mine, so hopefully he can continue on," he said. "Of course there's pressure, but you guys put it on us more than we do, so I've got no issue with it."
Young entered the week ranked 61st.
In other quarter-final play, second-seeded Ivo Karlovic of Croatia reached his third consecutive semi-final on Newport's grass courts, beating Switzerland's Marco Chiudinelli 6-3, 6-4.
The 37-year-old Karlovic said the hot, humid day with an abundance of sunshine made it tough. He was glad his match didn't last long.
"It was real difficult. It was hot today," the 6-foot-11 Karlovic said. "Last month I was in Europe and England and it was cool and almost cold, and this week earlier was cool, so today was pretty difficult. I was struggling a little there, but I was lucky that it was all done in two sets. The way I was playing, I'm pretty happy with that."
Karlovic served 16 aces and won 84 percent of his first-serve points.
"It always helps when you can hit a lot of aces, because this is my best weapon and that's my game - to have a lot of quick points, not a lot of rallies," he said.
Karlovic lost in the final the last two years.
In another quarter-final match, third-seeded Gilles Muller of Luxembourg rallied past France's Adrian Mannarino, the No. 6 seed, 2-6, 6-1, 6-2.
Marcos Baghdatis of Cyprus advanced to the semi-finals.
The semis will be played on centre court after enshrinement ceremonies for the 2016 class into the International Tennis Hall of Fame. Marat Safin and Justine Henin head this year's class.
Results Friday in the Hall of Fame Championships:
Ivo Karlovic (2), Croatia, def. Marco Chiudinelli, Switzerland, 6-3, 6-4.
Donald Young (8), United States, def. Steve Johnson (1), United States, 6-2, 6-3.
Gilles Muller, Luxembourg, def. Adrian Mannarino (6), France, 2-6, 6-1, 6-2.
Sam Groth and Chris Guccione (2), Australia, def. Ken and Neal Skupski (3), Britain, 7-6 (7/4), 7-5.
Jonathan Marray, Britain, and Adil Shamasdin, Canada, def. Purav Raja and Divij Sharan (4), India, 6-3, 6-4.