Fernando Verdasco was unable to continue Taylor Fritz's run of first-round exits as the American advanced in three sets.
Andrey Rublev has claimed some big scalps in 2019, but came unstuck against US Open runner up Daniil Medvedev in St Petersburg on Friday.
In his first outing since losing in the final at the US Open, Daniil Medvedev brushed aside fellow Russian Evgeny Donskoy.
Fourth seed Nikoloz Basilashvili overcame Andrey Rublev in three sets to reign in Hamburg for a second successive year.
Alexander Zverev wasted two match points in a semi-final defeat to Nikoloz Basilashvili, who will face Andrey Rublev in the final.
Splitting with Ivan Lendl does not appear to have had a negative effect on Alexander Zverev, who is through to the last four in Hamburg.
World number five Alexander Zverev appears to have found form at the right time heading into the French Open.
Novak Djokovic and Denis Shapovalov will do battle for the second time this year after the Canadian beat Pablo Carreno Busta.
Gael Monfils and Stefanos Tsitsipas both had to go the distance on Thursday to maintain their impressive winning streaks on the ATP Tour.
Roger Federer stayed in contention for a 100th ATP singles title in Dubai, but Roberto Bautista Agut and Kei Nishikori crashed out.