World number 14 David Goffin suffered a shock defeat to a player ranked close to 400 places below him as his return from an ankle injury at the Croatia Open hit a stumbling block.
Goffin was forced to retire in the third round of the French Open and missed the entire grass-court season, but a surprise 7-5 6-3 to 412th-ranked Ivan Dodig in his second match back would not have been in his plans.
The Croatian doubles specialist delighted the home crowd by dispatching of the top seed in 92 minutes, booking his place in the semi-finals - his first appearance at that stage in an ATP Tour event since 2013.
"I tried to be aggressive from the first point and tried to play shorter points. In the end, today was my day. I really felt good on the court and I was really aggressive," said Dodig, who will face lucky lose Andrey Rublev in the final four.
Rublev produced an impressive display to dispatch of third seed and reigning champion Fabio Fognini 6-7 (5-7) 6-2 7-6 (7-2).
Fernando Verdasco is the highest remaining seed in the Swedish Open after ousting defending champion Albert Ramos Vinolas 6-3 6-2 in the quarter-finals. Next up is another fellow Spaniard in David Ferrer, who saved two match points to edge Henri Laaksonen 7-5 3-6 7-6 (7-3).
Where Ferrer succeeded Karen Khachanov failed. The fifth-seeded Russian was unable to convert two match points in defeat to Alexandr Dolgopolov, while Diego Schwartzman bowed out to Andrey Kuznetsov.
John Isner remains on track for glory in the Hall of Fame Open following a 6-4 6-4 quarter-final win over Dennis Novikov, but fourth seed Pierre-Hugues Herbert was undone by Bjorn Fratangelo 6-2 5-7 6-4.