Dominic Thiem saw off Francisco Cerundolo for the second time in the space of a week as he dug deep in the deciding set to win 6-1 1-6 7-5 at the European Open.
The Austrian downed the Argentinian in straight sets six days earlier in Gijon but found this a sterner test of his capabilities against the sixth seed.
Nevertheless, the former US Open winner shook off a second-set collapse and then responded to going a break down in the decider, winning four of the final five games to seal a quarter-final clash with favourite Hubert Hurkacz.
He was joined in the last-eight by two more unseeded players, as David Goffin and Sebastian Korda recorded straight-set upsets over third seed Diego Schwartzman and fourth-ranked Karen Khachanov respectively.
At the Stockholm Open, fifth seed Alex de Minaur made swift work of American J.J. Wolf, dispatching him in a 6-4 6-2 win to set up a quarter-final with Canada's Denis Shapovalov.
Defending champion Tommy Paul is out however, losing to Sweden's Mikael Ymer, who recorded a 6-2 6-3 victory that earns him a clash with top seed Stefanos Tsitsipas.
Slippery court conditions contributed to a backlog in fixtures at the Napoli Cup, meaning first-round matches were followed by second-round encounters on Thursday.
Nevertheless, second seed Matteo Berrettini made light work of Roberto Carballes Baena, winning 6-4 6-2.
Roberto Bautista Agut, seeded third, slipped to a 6-4 6-4 loss to Mackenzie McDonald, with the American joining Berrettini in the last eight.