Federer, targeting a record-extending 10th victory in Halle, began his grass-court campaign with a maiden title in Stuttgart last week and extended his unbeaten winning streak on the surface to 19 matches with a 7-6 [7-2] 7-5 win.
Failure by Federer to win the grasscourt title would send rival Rafael Nadal back to the top spot going into Wimbledon which starts on July 2.
But the Swiss great has struggled at times in his run to Sunday's showpiece, again made to work hard as he downed Denis Kudla 7-6 (7-1) 7-5 in the last four.
World number one Roger Federer will aim to book his place in the semi-finals of the ongoing Halle Open, when he crosses swords with Matthew Ebden of Australia in their last-eight clash of the tournament here on Friday.
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Federer skipped the entire clay-court season for the second year in a row and is now just four wins away from matching Jimmy Connors' all-time record of 174 victories on grass. "I played Davis Cup there in 2006 and I know the courts and facilities there are excellent". "I think he served well and had a good mix and a good variety".
"I can take a lot a lot of positives out of today's match for the semis tomorrow".
A handful of errors from Federer opened up two break opportunities for Ebden and the 30-year-old Aussie rallied against Federer's backhand until he caved and fell 2-1 behind.
Ebden couldn't capitalise though, as Federer piled on the pressure with quick fire points to even the match at 5-5 and he served out a blistering 65-second game for a slender lead, but that was all he needed.