Wozniacki is looking for her third straight title in her home tournament in Copenhagen and broke the Croatian's serve twice in each set to wrap up the win in 1 hour, 8 minutes. She lost her serve once in the first set, but didn't face a break point the rest of the way.
"We played tennis on a high level today. Petra played a good match, she served well and put pressure (on me) the whole time," Wozniacki said. "She slices a lot, so there's no way out. She doesn't want to play long duels so I had to put pressure on her." Kerber beat third-seeded Jelena Jankovic 6-2, 6-1 in the other semifinal, breaking the former top-ranked Serb five times while never dropping the serve herself.
In Houston, World No. 10 John Isner beat defending champion Ryan Sweeting 7-6 (7/1), 7-6 (7/4) on Friday to reach the semifinals of the $442,500 ATP US Men's Clay Court Championship.
Isner, the second seed, fired 11 aces and saved all six break points that he faced in the all-American quarterfinal to improve to 19-6 for the season and keep alive his hopes for a first clay-court title.
Isner, a runner-up last month at Indian Wells, will next face Spanish third seed Feliciano Lopez, who led 6-4, 2-2 when Carlos Berlocq of Argentina retired injured.
Lopez is chasing his third ATP title and his first on clay.
The other semifinal will see Argentine fourth seed Juan Monaco, who edged South Africa's Kevin Anderson 7-6 (7/4), 7-5, take on US qualifier Michael Russell, who outlasted Ryan Harrison 6-1, 5-7, 6-3 in another all-American quarter-final.
Monaco, ranked 16th, won his fourth career ATP title, and first since 2007, in February at Vina del Mar and reached the semifinals last month at Miami, losing to eventual winner, world No.1 Novak Djokovic.
Anderson, ranked 33rd, was denied a chance for his second title in as many months after taking his second career ATP crown last month at Delray Beach, Florida.
Russell, a 33-year-old hometown hero, reached his first career ATP semi-final by holding off 19-year-old Harrison.
