The 153rd-ranked Groth defeated defending champion Nicolas Mahut of France 6-3, 6-4, and Karlovic edged Dudi Sela of Israel 7-6 (3), 7-5. The pair will meet on Saturday after inductions for the 2014 class into the International Hall of Fame, which is highlighted this year by Lindsay Davenport in the recent player category.
The other quarterfinal matches are scheduled for Friday.
The 26-year old Groth, who skipped the 2011 tennis season to play Aussie Rules football, was still excited to earn his first career ATP tour semifinal berth about 30 minutes after the match.
''It's a great feeling. I don't know how else to describe it,'' he said. ''I'm kind of at a loss for words right now. But for me, I don't think my tournament is over by any means. I'm going to come back out on Saturday with the confidence I can win my semifinal and win this tournament.''
Groth broke in a long third game of the second set that lasted 18 points - when Mahut double-faulted - to take control.
After losing three match points in the ninth game, he closed it out with an overhead smash and let out a loud, ''Yah!''
''I probably didn't even think about the match until we had that long game in the second set,'' he said. ''For the first time everything became a little bit real.''
In the other match, the 6-foot-11 Karlovic had nine aces and won 39 of his 46 first-serve points to gain his third semifinal this season.
''It was real difficult,'' he said. ''He was playing real good and keeping the ball low, which I don't like, and it was real hot today. I'm real happy that it went two sets.''
Karlovic held at love, collecting one ace, to go up 6-5 in the second set. Sela then double-faulted on the seventh point of the next game, setting up match point. On the second serve, Karlovic then hit a deep forehand return that Sela backhanded into the top of the net.
The fourth-seeded Mahut made his ninth appearance on Newport's grass courts, the most of any player in the field. He was denied his 50th career victory on grass.
''I was little bit tired. I played a lot from clay (season), and I played the whole grass season,'' he said. ''The thing is he played well. To win I had to play my best, and that was not the case today.''
Mahut, who collected the most grass-court victories on the tour last year with 12, entered the week ranked 59th. He had won seven straight matches at Newport.
- Sports & Recreation
- Nicolas Mahut
- Ivo Karlovic
- Samuel Groth
- Dudi Sela