KEY BISCAYNE, Fla. — Mardy Fish claimed the top U.S. spot for the first time Wednesday by reaching the semifinals of the Sony Ericsson Open when he beat No. 6 seed David Ferrer 7-5, 6-2.

KEY BISCAYNE, Fla. — Mardy Fish claimed the top U.S. spot for the first time Wednesday by reaching the semifinals of the Sony Ericsson Open when he beat No. 6 seed David Ferrer 7-5, 6-2.

The 29-year-old Fish will climb to at least 11th, a career best, in the next world rankings. Andy Roddick, a good friend since childhood, will fall from eighth to 14th after losing his opening match last week.

"I don't think I would ever feel like I was the No. 1 American," Fish said. "Andy has had a pretty good career. You can put his career on top of mine about six times. He's always going to be the top dog in my generation."

But Fish is the lone American with a shot at the title this weekend. He'll try to continue his best run in 10 appearances at Key Biscayne on Friday against No. 2-seeded Novak Djokovic, who is unbeaten this year.

Djokovic extended his winning streak to 24 consecutive matches by defeating former University of Illinois star Kevin Anderson 6-4, 6-2. Djokovic won two Davis Cup matches in December, and his 22-0 record in 2011 is the best to begin a year since Ivan Lendl started 25-0 in 1986.

Victoria Azarenka advanced to her first semifinal this year by beating two-time champion Kim Clijsters 6-3, 6-3. Clijsters, nursing a right shoulder injury since she won the Australian Open in January, had eight double-faults and held only three times in nine service games.

"I just didn't feel good out there," Clijsters said. "I didn't have any fighting spirit. Against some lower-ranked players maybe it's possible to get through matches, but against somebody like her, it's not."

Azarenka's opponent tonight will be No. 3 Vera Zvonareva, who beat No. 9 Agnieszka Radwanska 7-5, 6-3.

Fish was braced for an endurance test against Ferrer, a dogged baseliner, but the Spaniard had back-to-back double-faults to lose serve and fall behind 6-5 in the first set, and Fish pulled away from there.

Ferrer, who lost just 12 games in his first three matches, said he was bothered by indigestion.