Federer thrashed Alexander Zverev to win his ninth title at the Gerry Weber open on Sunday and has still only lost two matches this year en route to four titles, including the Australian Open in January.
Federer won 6-3, 7-5 last spring at the Rome Masters before Zverev pulled off a 7-6 (4), 5-7, 6-3 upset in the Halle semifinals.
The Swiss maestro will now face Karen Khachanov, who won his all-Russian quarterfinal match-up against Andrey Rublev 7-6, 4-6, 6-3 to reach his first tour semifinal of the year.
The top seed suffered a shock loss to veteran German Tommy Haas in his first competitive match on grass this season in Stuttgart, but has built momentum in a tournament that has given him such fond memories over the years.
Federer will now surely start Wimbledon as favourite in search of his eighth title, having been cut to 2/1 by Sky Bet.
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Federer described his Halle Open final opponent as a tough player to play against and described his serve as wonderful and his backhand as one of the best in the game. The first set went to a tiebreak, which Federer won before he took the second 6-4 for a straight sets victory.
"I as very calm out there, even in hard moments". He improved his Halle record to 57-6. The Swiss then fended off set points at 5-6 before closing out the match in a breaker. "He takes big cuts at the ball, returns very well".
However, he was defeated by Alexander Zverev in three sets in the semi-finals at Halle in 2016.
Federer, who hit 11 aces and 32 winners, said facing Khachanov on Saturday will present a new challenge for him. "I do not know if I will ever be going to win this tournament again so I will enjoy this one".