Roberto Bautista Agut's hopes of reaching the ATP World Tour Finals were dealt a blow when he suffered a stunning loss to Alexander Bublik in the Kremlin Cup but David Goffin moved into the quarter-finals of the European Open.
Bautista Agut pieced together a surprise run to the final of the Shanghai Masters last week before he was beaten in a showdown with Andy Murray.
The Spaniard is still in with a chance of featuring in the season-ending ATP Finals in London, but suffered a setback on Thursday when he went down 6-2 7-5 to Russian qualifier Bublik in the second round.
Teenager Bublik is ranked 266th in the world, but the 19-year-old pulled off a major upset at the expense of the two-time Kremlin Cup runner-up.
Bautista Agut was broken six times and won less than half the points on his serve to make an early exit.
Daniil Medvedev also defied the odds in his homeland, claiming the scalp of fourth seed Viktor Troicki after coming from behind to win 3-6 6-3 6-1, but Philipp Kohlschreiber made it through and Pablo Carreno Busta advanced when Damir Dzumhur retired.
Goffin can leap to ninth in the Race to London with a win on home soil in Antwerp this week and the top seed reached the last eight by getting past Florian Mayer 7-5 6-4.
David Ferrer had a day to forget, with Kyle Edmund sending the second seed packing with a 6-1 3-6 7-6 (7-3) win after coming from 5-3 down in the final set.
Gilles Simon, the fifth seed, bowed out with a 6-4 6-4 loss to Jan-Lennard Struff, while Marius Copil marches on along with Diego Schwartzman.