HALLE - Roger Federer reached the Halle grass-court final for the 10th time after beating giant Croatian Ivo Karlovic 7-6 (7/3), 7-6 (7/4) in Saturday's semi-finals. The Swiss, who has won the title seven times, will go on to face Italy's Andreas Seppi, who advanced at the expense of Kei Nishikori after the Japanese world number five retired injured when trailing 4-1 in the first set.

World number two and top seed Federer needed two tie-breaks to claim a 13th win in 14 meetings with Karlovic. The Croat, who stands 2.11m (6ft 11in) tall, had battered down 45 aces in his quarter-final victory against Czech Tomas Berdych on Friday but against Federer he managed a mere 21. "It is always difficult to play against Ivo but the important thing was that I remained calm," said Federer, who also recorded his 50th career win at the grass-court event. "I was very lucky in the first set and so I'm all the more delighted to be in the final again."

The only consolation for the 36-year-old Karlovic was that he did not lose serve all week in 48 games and ended the tournament on 114 aces.

Federer is chasing a 15th title on grass -- and fourth overall in 2015 after Brisbane, Dubai and Istanbul -- as he warms up for Wimbledon, which begins on June 29 and where he's been champion on seven occasions. Seppi, the world number 45 who last won a title in 2012, was in control of the first set of his match against Nishikori when the Japanese succumbed to a calf problem.

Seppi won his quarter-final against Gael Monfils on Friday when the Frenchman retired injured in the second set after crashing into an advertising board beside the court. Federer has only lost once in 12 previous meetings with Seppi, although that came in the third round of this year's Australian Open. "I played him many times. For some time, we also practiced quite often. I think he hits the ball very well on both sides, especially cross court and then he can go down the line," said Federer of the Italian.

"I think that's what makes him a tough player. I think fitness-wise he's very fit, you know, he won't go away. He doesn't have the best second serve but I think he has improved that over time. And because he hits the ball quite flat it actually helps him on the grass." Nishikori said he had felt his calf injury during his quarter-final win over Jerzy Janowicz on Friday but opted to retire on Saturday with Wimbledon fast approaching.

"I felt it yesterday during the quarter-final and I fought through it. But there was a little pain this morning and I tried in the match, but couldn't really move," said 25-year-old Nishikori. "I don't want to take a big risk for Wimbledon, so I just retired from the match." Nishikori, who enjoyed his best Wimbledon performance in 2014 when he reached the fourth round, said he was hopeful that the injury will not be serious. "I cannot say much because I have to see how it will be the next couple of days. But I'm sure it's going to be okay. It's no big deal," he said.