Felix Auger-Aliassime eased through to his fourth ATP quarter-final of the season in Cologne, beating qualifier Henri Laaksonen 6-4, 6-1.
But former US Open champion Marin Cilic was on the receiving end of a 3-6, 7-6, 6-2 loss against young Spaniard Alejandro Davidovich Fokina.
Davidovich Fokina is through to the second ATP quarter-final after Estoril last year.
Roberto Bautista Agut defeated Gilles Simon 6-4, 7-6 in two hours and 19 minutes to also make the quarters.
It was the first victory for Bautista Agut over Simon since 2013.