"I think the second half of the season is going to be really, really interesting".
Zverev's first serve seemed inconsistent and Federer broke at 4-4 in the second set to break the German, before serving out the match.More news: London's Grenfell tower fire started with faulty fridge: Scotland Yard
Federer is through to the semifinals in Halle for the 13th consecutive time, with his two quarterfinal losses at the event coming in 2000-2001. He's a tough customer, plus he's the defending champion. The grass court season did not start the way Federer would have wanted as he suffered an early exit at the Stuttgart Open but the Swiss looks like he is back to his best now.
Again the Swiss had the chance to close out the match with Mayer serving at 3-5, but in the end, Federer had to do it with balls in his hand, and did so easily, 6-4.
Federer has won all seven of his career matches against Mayer, including three straight-sets wins in Halle. They are the sets you need to win to win tournaments.More news: Queen's Speech axed to make way for complex Brexit talks
The 19-year-old Rublev, who received a wild card for the grass-court tournament, will face another Russian in Karen Khachanov in the next round.
Federer is 7-0 against the world No. 134. "He plays a bit different on the serve and the forehand, which is different to the regular forehand technique we see".
"I've played one set against him in practice this week".More news: Trump calls Warmbier's death a 'total disgrace'
Another quarterfinal will pit Alexander Zverev against Roberto Bautista Agut. "And playing against me, all are always very motivated", Federer told the Halle Open website. It's a match I will most likely have to focus on my own game, make sure I serve well because he can go through spells where he can serve big and well.