In the last downhill run, the Swede, who pulled hard on the sprint lap, lost the inside track and Arnd Peiffer was able to dodge past and keep away from the short run.
Ponsiluoma accounted for personal best after two previous third places in the World Cup.
Ponsiluoma shot full in the fourth shot and went out in the lead just before Arnd Peiffer.
Emelien Jacquelin and Benedikt Doll had a small gap until the close duo.
The Swede pulled hard on the sprint lap and had Peiffer in the back towards the riot.
In the third shot, Ponsiluoma, who had a boom in the first shot, answered for full house and went out as second after Sturla Holm Lägreid.