By Theo Ruizenaar
ROTTERDAM (Reuters) - Top seed Roger Federer struggled to defeat Finn Jarkko Nieminen 7-5 7-6 on Friday to reach the semi-finals of the World Indoor Tournament.
The Swiss, who is this week making his first appearance in the Dutch port city since he won the title in 2005, lacked rhythm against the unseeded Nieminen.
Former world number one Federer came back from 40-0 down in the 11th game to break serve on the indoor carpet and then had to rely on the tie-break to clinch victory in the second set.
"It was a tough match but important to get through," he told reporters. "I am still getting used to the surface and tonight I struggled with my timing in the rallies.
"But I also have to give credit to Jarkko the way he played. He was really aggressive and even on his second serve he kept attacking."
Federer, the world number three, next meets Nikolay Davydenko after the unseeded Russian put out fifth-seeded Frenchman Richard Gasquet 7-5 6-3.
Second-seeded Czech Tomas Berdych also went through with a 6-3 6-4 triumph over Italian Andreas Seppi.
Berdych now faces third seed Juan Martin Del Potro after the Argentine thrashed seventh-seeded Serb Viktor Troicki 6-0 6-1.
(Editing by Tony Jimenez)