Roger Federer booked his 12th career final at the ATP Halle grass tournament on Saturday, beating qualifier Denis Kudla 7-6 (7/1), 7-5.
The Swiss needs to win the title on Sunday - it would be his tenth at the event - to remain world number one heading into Wimbledon.
He will face either Spanish fourth seed Roberto Bautista Agut or Croatian Borna Coric.