Goffin finally managed to hold serve in the second set, but Dimitrov still was able to break the Belgian's serve two more times.
"I have so much fun playing in London and I have been so successful here".
"It was a good battle and I always enjoy myself at this handsome arena", said Federer, who became the first to reach the final four at this year's tournament. What I like about Zverev is he's got the full package... the last six months of the season have given him everything he needs to work forward to... With his win over Zverev, he secures his place in the semifinals.
The No. 8-seeded player defeated Wimbledon finalist Marin Cilic 5-7, 6-2, 7-6 (4) on Tuesday.
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Unfortunately for the Lazio frontman, he was forced to shoot from a tight angle and could only fire into the side-netting. It's the first time the Swedes have made the World Cup since 2006, leaving just three spots to still be decided.
Federer has lost twice to Zverev on tour, and once in the Hopman Cup, and believes the German will be a major threat to the game's elite for years to come - and perhaps to him again even as early as Sunday.
"I'm not the type of guy that will just enter a draw and be happy to make the third round or the quarters or whatever".
Zverev, who won his opening match against Cilic, will face Sock on Thursday to decide who will join Federer in the final four.
"It was a very positive match for me", said the man from Hamburg.