Ewan finished with the two riders who are expected to feature in the sprint stages, Andre Greipel (Lotto Soudal) and Giacomo Nizzolo (Trek-Segafredo) at the end of the 206km leg along the northern coast of Sardinia, from Alghero to Olbia.
It was the second podium for 22-year-old at the Giro. He also finished second last year in Bibione (Stage 12) in his debut at the Italian race.
"It was a really strong move by Pöstleberger," Ewan said. "It was a hectic finish and sometimes a moment’s hesitation can lose the race."
"There are not many opportunities to take the pink jersey so obviously it's bittersweet to finish second but there are more days to come and you have to congratulate the move.”
A crash towards the finish disrupted the sprint trains and that may have been the decisive factor in Pöstleberger's win.
"We need to look at the footage. It looked like an accidental move by Bora but it paid off," sport director Matt White said.
"The finish was hectic after a crash in the final kilometres and maybe there was some hesitation. Sometimes that's all it can take in a situation like this.
"It's the first sprint of a Grand Tour after a relatively slow day. We are all feeling each other out and they aren’t often textbook sprints in those scenarios. There are more opportunities to come.”
Stage 1 Velon Data Summary for Caleb Ewan (Orica-Scott) – 2nd place.
He's light, he's aerodynamic, he's fast and powerful. Despite his small build for a sprinter, Caleb Ewan displays a very high absolute power output.
- Sprint: Time: 17sec
- Speed: 64.3km/h (Max Speed: 70.9km/h after 12sec – very fast Sprint)
- Power: 985W (Peak Power: 1484W right before he hits top speed)
The 221km second stage from Olbia is not well suited to Ewan and the sprinters and is classified as a medium mountain effort with 2,800 metres of climbing, including a second category rise which lasts for 26.6km before a long descent to the finish and a final flat 10km. This may give the fast men an opportunity to regroup for the finale in Tortolì but should better suit a rider like his compatriot Nathan Haas (Dimension Data).