Antonio Lindback won an incident-packed FIM Speedway GP of Torun, while Chris Holder claimed his first world championship.
Going into the season finale, Holder was leading Nicki Pedersen by two points and had extended his lead to six points - with a potential nine points up for grabs - when the pair met in the second semi-final.
There was drama when Pedersen, racing from Gate 2, got to the first bend ahead of Gate 1 rider Holder, who straightened up and Pedersen was sent to the shale.
Referee Craig Ackroyd controversially allowed all four riders back, with Pedersen unhappy with the decision and he clashed with Holder on the track, with the pair having to be separated.
Holder was calmed down by former world champion and compatriot Jason Crump, who was retiring from GP racing at the meeting, and he had the best start in the re-run to win, sparking wild celebrations among supporters, while Pedersen finished third.
In the final, Holder had the best start but suffered mechanical failure on lap 2 and retired. All three remaining riders had a chance to win but Lindback emerged the victor ahead of Tomasz Gollob and Greg Hancock to claim his second GP win of the season and move into seventh in the overall standings.
Holder was delighted with his 'unbelievable' world title, which came after he had claimed only four points from the opening GP in New Zealand.
Thanking his pit crew and family, he said: "I was ready to quit (after New Zealand) and I was scratching my head pretty big and I had no answers for that really apart from I put it down to Max (his son) being born.
"I know a lot of Aussies are watching this back home and it was worth it to get up for that one eh!"
"This isn't going to sink in for a long time and I've got to thank Jason too, he's been here and done that so many times before.
"He grabbed me - we had a chat before the semis and after the little first corner incident we had another chat and he just kept me cool," said Holder, adding there had been no 'bigger pressure than that.'
Three-times world champion Pedersen congratulated his rival afterwards but felt Holder should have been excluded.
He said: "It's tough. I respect Chris very much, he's been the best all night but I trumped him in the semi-final.
"I knew I had to win over him and I did it and he went over the white line and he pushed me hard and I don't know what the referee saw up there so I'm disappointed by that."
Holder ended up collecting the world title by eight points from Pedersen with 160 points, with last season's champion Hancock 12 points off the summit.
Gollob earned 21 points on the night to take fourth overall, ahead of Emil Sayfutdinov, Crump, Lindback and Fredrik Lindgren in eighth.
British rider Chris 'Bomber' Harris earned six points from the meeting, including a morale-boosting win in his final heat. He finished 12th overall and must now wait to see if he gets chosen by organisers to race again in the series next year.