The Polish Eagle, who bagged his first in February 2018 a season before he'd even earned his maiden PDC Tour card, led 7-5 only for Diamond to pull one back before a stunning 155 checkout completed a match-levelling 12-darter.
White was now throwing for glory in Wigan but Ratajski was not to denied and despite agonisingly missing the bullseye for a show-stopping 170 checkout in the decider, he came back to finish the remaining 25 as his opponent waited on 16.
The 43-year-old was in electric form throughout the day, averaging over 103 in four of his six matches en route to the final, including a high of 106.5 in a high-class 6-4 victory over Gabriel Clemens in the last eight.
"But then I played very well with averages over 100 and I feel very comfortable with the new darts I am playing with. I hope this will be my best season. Last season was brilliant and I hope this one will be even better."
White, who was chasing a 14th career title, had survived three match darts in the deciding leg of a dramatic semi-final with world champion Wright, who averaged 103.8 compared to Diamond's 97.1.
Apart from that - and also being taken the distance by Alan Tabern in the last 32 - the 49-year-old enjoyed a relatively comfortable route to the final, beating Mensur Suljovic (6-3), Jamie Hughes (6-4) and Martin Schindler (6-3) without the need for a 100+ average.
His best statistical performance came in the very first round when recording a mark of 107.6 in a 6-3 triumph over Jan Dekker.
Van Gerwen's 6-4 loss to fellow Dutchman Noppert in the quarter-finals means he's still searching for his first title of 2020 although he did produce a pair of sparkling displays when beating Gary Anderson 6-3 with an average of 107.4 and Ryan Murray 6-2 with a spectacular mark of 110.9.
Last 16
Quarter-Finals
Semi-Finals
Final