The Swede, who twice prevailed against Schumacher’s seven-time world championship-winning father Michael in the 2007 and 2009 finals, beat the ex-Haas F1 racer two-nil in the final.
Ekstrom booked his passage to the final by defeating US rallycross ace Travis Pastrana in the first round, then overcame five-time World RX champion Johann Kristoffersson in two tight quarter-final encounters.
That put Ekstrom into a semi-final battle with Hyundai World Rally Championship driver Thierry Neuville. The heats between these two also went down to the wire, but the 2016 World RX champion prevailed, helped by his Belgian adversary knocking the steering out of line in the second clash.
The other semi-final had pitted Schumacher against recently-retired Aston Martin F1 driver Sebastian Vettel, his fellow Team Germany driver from Saturday's Nations Cup.
Schumacher gained the upper hand in the first heat, where Vettel hit a snow bank and ended up with his Supercar Lite on the wrong side of the track. That lost him the race and gave Schumacher a psychological advantage going into the second encounter, which the younger German duly won.
The final opened with a battle in Polaris RZR machines, and Ekstrom nicked victory by 0.348s. He was more convincing in the second clash, which saw the rivals switch to the Supercar Lites. Ekstrom won it by over a second, despite a small fire breaking out in the cockpit.
Earlier, hot favourite Oliver Solberg was eliminated in his quarter-final against Neuville. Jumping into the ultra-powerful FC1-X Nitro rallycross machine for the first time, the Nations Cup winner pushed a little too hard and collected an advertising banner approaching the bridge, so went into the second heat with the maximum 10-second deficit.
He could only hope for a similar mistake from Neuville, but this never came and Solberg had to console himself with the fact that he had edged his father and 2003 WRC champion Petter in the eagerly awaited first-round clash between the Nations Cup victors.
Defending Race of Champions winner Sebastien Loeb lost out to Neuville in the first round, although the rally aces shared the wins and a tie-break was needed to eliminate the nine-time world champion.
