Roger Federer felt he played his best tennis of the week at the Gerry Weber Open as he moved within one match of a stunning 11th final appearance in Halle.
Top seed Federer, who is seeking his ninth title at the grass-court tournament, beat David Goffin 6-1 7-6 (12-10) on Friday to set up a last-four meeting with rising star Alexander Zverev.
Goffin was well beaten in the opening set, but served for the second only to pass up the opportunity.
A satisfied Federer said: "I thought it was my best match thus far. It is a good win for me and I'm clearly very happy to be in the semis."
Assessing the threat posed by 19-year-old Zverev, a 7-6 (11-9) 6-3 winner over Marcos Baghdatis on the Cypriot's 31st birthday, Federer added: "He's got a big serve, he's got a nice backhand, he's improving his forehand and he's moving forward.
"He's going to be a tough player in the future, no doubt about it."
Zverev saved five set points in the opener against Baghdatis, a runner-up in Halle back in 2007.
Saturday's other semi-final will see Dominic Thiem, who beat Federer on the way to winning last week's Stuttgart Open, face Florian Mayer.
Thiem was handed a walkover in his quarter-final when Philipp Kohlschreiber withdrew with a left hip strain, while Mayer beat Andreas Seppi 7-6 (7-4) 6-3.