He earned a 12-10, 15-17, 11-8, 11-8, 16-14 win over Anton Kallberg of Sweden having been taken the full distance in his two previous matches against Britain’s Paul Drinkhall and fellow German Benedikt Duda.

Boll’s next opponent as the tournament concludes tomorrow will be Sweden’s top seed and 2019 world silver medallist Mattias Falck.

The world-ranked number eight player was the first to reach the singles semi-finals in Warsaw.

Falck beat fellow Swede Jon Persson 11-2, 11-7, 12-10, 11-6.

Meanwhile Boll’s compatriot Dimitrij Ovtcharov, like Boll a former number one and seeking a third European title, reached the last four the hard way with an 11-7, 11-7, 11-9, 9-11, 7-11, 9-11, 11-8 win over Lobomir Jancarik of the Czech Republic.

Jancarik had earlier beaten highly-rated French player Simon Gauzy in straight games.

Ovtcharov’s next opponent, Marcos Freitas of Portugal, had a more straightforward progression to the semi-finals with a 5-11, 11-5, 11-5, 11-9, 11-6 win over Ovidiu Ionescu of Romania, men’s singles silver medallist in 2018.

Five German and five Swedish players had reached the last 16.

In the women’s singles 25^th seeded home player Natalia Bajor fell just short of reaching the quarter-finals as second seed Petrissa Solja of Germany eventually beat her 16-18, 8-11, 11-2, 11-8, 9-11, 13-11, 11-9.

Solja’s compatriot Sabine Winter, seeded 37th and one of the few qualifiers left in the title race, beat the number three seed Han Ying in an all-German encounter 11-9, 12-10, 9-11, 11-9, 12-10.

Linda Bergström of Sweden also reached the last eight by beating Slovakian mixed doubles runner-up Barbora Balazova in convincing fashion 11-9, 11-8, 11-8, 11-4.

Balazova and partner Lubomir Pistej were beaten 11-9, 11-8, 11-6 by Germany's Qiu Dang and Nina Mittelham.