He will now face rapidly rising talent Karen Khachanov, who won his all-Russian quarter-final against Andrey Rublev 7-6 (8) 4-6 6-3 to reach his first tour semi-final of the year.
Yet to drop a set in the event so far, the 18-time Grand Slam victor will be looking for his fourth title of the year and ninth Halle title before hoping to achieve his main goal of winning Wimbledon.
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. Khachanov then missed two set points before Federer took it to the tiebreaker.
He faces Alexander Zverev, the promising German, who beat Richard Gasquet 4-6 6-4 6-3. According to odds makers, the 35-year-old Federer enters the 2017 Wimbledon as the favourite, closely followed reigning champion Andy Murray, Rafael Nadal and Novak Djokovic.
But he quickly fell behind in the second as Zverev, a finalist previous year, who has already won three titles in 2017, charged to a 4-2 lead and held on to take the set.
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Boston sent its first overall pick to Philly in return for the No. 3 overall pick and future draft picks. They drafted Ben Simmons No. 1 a year ago , Allen Iverson in 1996 and Doug Collins in 1973.
Federer, will be seeded ahead of his Spanish rival for Wimbledon, which starts in eight days.
The Swiss Maestro needed 90 minutes on the grass courts of the German city to defeat Zverev, who had dumped Murray out of the Australian Open in the fourth round earlier this year.
His huge serve was on full display when he won the 's-Hertogenbosch title on grass last week and once again he used it to devastating effect against Querrey.
Federer also spoke about his straight sets victory over Mischa Zverev, who is at a career-high ranking of 29.
The pair held serve for nearly two hours before Zverev managed the first break of the match early in the third set and the 20-year-old broke again two games later to finish the Spaniard off. "Probably it's one of the dream finals of the tournament and I'm very much looking forward to it". "I'm still just very happy how I was able to close it out in the breaker".
"I as very calm out there, even in hard moments". "He started serving great, which put me under pressure as I wasn't getting many looks".