David Ferrer was left shaken when a man forced a stoppage in his Swedish Open semi-final against Fernando Verdasco by invading the court and shouting Nazi slogans.
The individual walked onto the area of play early in the second set of the encounter and shouted "Hell Seger", a Swedish translation of the Nazi motto "Sieg Heil", with his right arm raised and fist clenched.
Play was stopped by the umpire before the person, who was roundly booed by the crowd in Bastad, was shepherded away.
Ferrer went on to claim a 6-1 6-7 (3-7) 6-4 victory over his fellow Spaniard, but found the interruption "upsetting".
He told a post-match press conference: "It was not good this incident. Sometimes it's dangerous because you never know who the guy on the court is.
"Security is important for the tennis players and everybody and we don't [want] to see these incidents.
"I was scared when he was talking about that. This guy is a crazy guy - I don't know exactly but it's a little bit upsetting, it's not normal doing that.
"Tomorrow [Sunday] we are going to have more security.
"This is different [to a streaker]. One guy saying 'Heil Hitler' and these type of things, it's dangerous, it's not normal."
Ferrer will face Alexandr Dolgopolov in Sunday's final.